69 Replies Latest reply on Aug 7, 2014 8:58 AM by IMTAPASPANI

    Have a question about LEDs or LCDs? Ask the expert, Brian! [Archived]

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        • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
          edmund

          Hi,

           

          one of the key consideration of producing High brightness LED is the packaging form since the packaging must be design in a way that enable to dissipate heat effectively and emit light in a efficient manner

           

          Thus, May I know the current process/factors of fabricating High Brightness LED.

           

          1) The type/material of encapsulation such that it is enable to dissipate effectively and emit light efficiently

           

          2) Any current research on producing a higher wattage HB LED.

           

          3) Methods of emitting light from LED in a more effective way.

           

          Cheers

            • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
              bkcoates

              The questions submitted is a little tough to answer without giving away a certain amount of proprietary information.  So unfortunately, I will have to answer them in fairly broad terms.

               

              1) The type/material of encapsulation such that it is enable to dissipate effectively and emit light efficiently: As you stated earlier, heat plays a huge role in determining encapsulation.  Most manufacturers of HB LEDs use a 2 optic/encapsulate technique. The primary optic (the encapsulate that interfaces directly with the die and wire bonds) must have a coefficient of thermal expansion similar to that if the LED and the bond wire.  The secondary optic is optically clear within the wavelengths of emission as well as consistent enough to not discolor during high heat, such as soldering.  As you may recall, a manufacturer had issues with their primary optics failing under certain circumstances not too long ago.  This is a crucial step not to be rushed.

               

               

              2) Any current research on producing a higher wattage HB LED.  The actual die manufacturers are constantly pushing the wattage envelope.  Generally, the easier way to accomplish this is to simply make the die larger.  Making the die larger is not as simple as I make it sound.  They have to be able to pass higher currents efficiently which demands that the manufacturing process be very tightly controlled as to create die that are orders of magnitude larger but have nearly identical construction (no thin film variances can be allowed to avoid generating waste).  Of course, the challenge then becomes conducting the extreme amounts of heat created away from the die to keep it stable.  Generally, most packagers will use a multiple emitter setup to create a higher wattage component.  A 10W point source emitter is not a practical as a 10W emitter from a 1" circular surface (at this point in time).  This point leads into the next question.

               

              3) Methods of emitting light from LED in a more effective way. This point is important from an integrators standpoint.  The actual packaging does play an important role in this, but what do you do with a 100 Lumen 1W emitter once you have one?  Do you want to create a spotlight or are you making general illumination?  Is it a security/warning light?  There are lots of application specific questions that can not only shape the packaging of the die itself, but the finish product you expect the component to fit into.  This is the discussion of view angle versus brightness.  You can create a component that emits 200 Lumens with a 10 degree half angle, or you can create a 100 Lumen source with a 75 degree half angle.  Each has a benefit in a specific application; although wider view angles tend to be more general use as tertiary optics could be used to fine tune the final good.

               

              I'm afraid my answers will only lead you to more questions, but that is about as specific as I can get without building a product for you.

                • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                  inventor11

                  Hi Brian, I have a LED circuit that uses a CD4017 sequencer driving the base of 2N3904's, collectors are connected to VCC 9 v. and the emitters go through a 360 ohm resistor to the anode of the LEDs - cathodes all connected to GND. The circuit works fine driving 5 to 10 LEDs from each IC output through the transistor and goes through the cycle and starts over.  But, I want to drive up to 50 LEDs per CD4017 output (7) and was told to use a IRLD014PBFIRLD014PBF MOSFET which has 1.7 amp capability in place of the transistors.  It works fine, but the LEDs will NOT turn off after the signal turns off from the IC.  I have a resistor (have tried several values) from IC output to the G, and the S to VCC 9 v. and the D through a 360 ohm resistor to the anodes,

                  the cathodes go to GND.  Please help with what I'm doing wrong - thank you

                    • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                      bkcoates

                      Wayne,

                       

                      It is difficult to say exactly given that I do not have the circuit in front of me.  It sounds like, with your first circuit, that your set up is sound.  That said, it sounds like to me that the MOSFET is not getting biased properly to turn it off.  I do not know what your level of expertise is when it comes to electronics, but as similar as npn and MOSFET transistors are, they are just different enough to be troublesome and thus correctly biasing the FET will allow you to turn turn the circuit off when you send the off signal from your driver.

                       

                      Best regards,

                      Brian

                        • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                          inventor11

                          Hi Brian, thanks for your reply.  I've been in electronics for 40 years, but as a mechanical engineer, altho, I have picked up quite a bit of electronic knowledge, but not about biasing a MOSFET. Please go to http://www.electronicsforu.com/electronicsforu/lab/ and click on S No. 170 for the schematic.  I'm wanting to replace the 2N3053's with the n-ch IRLD014PBFIRLD014PBF 1.7 amp to drive more LED's. I am not making the "welcome" sign but some other designs that could use 50 LED's per leg.  I know that it's not a good idea to not have a limiting resistor for each LED, but a resistor really draws down the voltage to the LED.  Thanks again for your great help!  Have a great day, Wayne   

                    • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                      valfitzandrew

                      Brian

                      I have an RV which has 12V lighting. The fixtures use clear tail light bulbe and they draw lots of current and don't last very long. I have been trying to find a suitable led that works. No luck to date. I think I need cree leds perhabl 2 or 3 emitters and pointed parallel to the mount axis. They should have an emit angle of approx 120 degrees. Do you know of such an animal?

                      Thanks

                      Val

                        • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                          bkcoates

                          John,

                           

                          Your best bet is to find pre-made lamp replacement devices.  These have the necessary components internally to allow the LEDs to operate at the necessary voltage levels in certain applications, 12V being yours.

                           

                          Fortunately, 12V DC applications are the simplest and easy to deal with on your own.  They simply require only a resistor in addition to the LEDs and the packaging.  The simplest case is 3 LEDs in parallel -> resistor -> 12v power.

                           

                          The harder part is finding an emitter that has enough brightness and a wide enough view angle to fit your needs. Another consideration is how much power is available from the 12V source.  There are some very powerful emitters out there these days.  These emitters, in the LED world, are referred to has high powered.  This is a bit of a misnomer because LEDs are still lower power when compared to incandescent bulbs.  These emitters go from 1W (3V@350mA) to as high as 10W in some cases.  These high power emitters do need some form of thermal management in order to not fail early though.  You can find examples of these products here and here.

                           

                          Best regards,

                          Brian

                            • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                              valfitzandrew

                              Thanks for the info Brian. My RV has over 400 amp hour of battery available to the house. We have a genset to replace what is used so available DC isnt the issue. I am trying to lessen the load and provide better light while extending the service life of the bulb. All possible with the hipower led's. My lamp fixtures are 1156 bases and are fairly deep (a[[rox 1.5") inside the shade. I have purchased single samples of bulbs with multiple emitters in the end with unacceptible results. Same goes for those lights with emmitters built up along the long axis of the bulb. I had hoped that you would be a fount that steered me to a solution. In the meantime I have purchased a gender changer 1156 to parallel pins and samples of hipower bulbs to try. This is, of course, a lot of trouble for only 12 fixtures, but one I think worth the effort as in our previous home one night with the outside entryway light left on flatted one deep cycle battery with 90 ah capacity. Dont want this with this coach.

                                • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                  bkcoates

                                  John,

                                   

                                  I agree that what is widely available today in the market place has not quite lived up to the standards to which we've been accustomed in terms of brightness and color quality.  I have seen some pretty good looking products, on paper anyway, coming from Phillips/LumiLEDs and OSRAM/Sylvania in terms of Edison based home light bulb replacements.  Both companies have a track record in both lighting and the LED market.  I haven't been on the lookout for 1156 replacements, but what I have seen from some Chinese companies has not excited me.

                                   

                                  I'm sorry I couldn't have steered you into a more specific direction.

                          • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                            cropcircles

                            Brian could you provide some feedback regarding LED vs LCD and how it applies to gaming PC's. Which is better regarding quality, lighting, longevity and any other professional information that would be helpful. Having some discussion over at Neowin forum and need some expert opinion on current technology.  Thanks Brian.

                             

                            http://www.neowin.net/forum/topic/890622-lcd-vs-led-monitor/

                              • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                bkcoates

                                Rodney, I can comment here for you.  There was a poster that replied to that thread who is 100% correct.  The phrase "LED TV" is misrepresentative of the technology used.  LED refers to only the backlight used to shine through the LCD.  Older models of LCD TVs use CCFL, which is a type of fluorescent.  Those aren't as bright as LED and degrade a lot faster than LED backlights.  The contrast that you will receive with a so called "LED" TV will be much better.  Also, for smaller screens (say less than 23" approximately) "LED TVs" use less energy than the older types, but for larger screens (think 32" or greater) the LED system will actually draw more energy than your older TV.

                                 

                                There is a newer technology in OLED displays, but these are not popularized yet.  They have a shorter functional life and haven't been commercially built in many sizes beyond that of an 11 inch display, if any.

                                  • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                    cropcircles

                                    Thanks for the feedback. The primary discussion was in regards to PC monitors and not TV's not sure if it matters, however in relation to PC gaming and the use of Geforce/ATI cards that can display incredible amounts of displays at increased frame rates. My question would be more specific to which PC monitor LED or LCD would perform best under gaming conditions using quad-core and above processors and high end video cards.

                                     

                                    http://www.damtodam.com/

                                      • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                        bkcoates

                                        Ok, well you question comes down to response time, resolution, contrast (dynamic or otherwise) and color quality.  In today's marketplace, the response time of the pixel is a moot discussion point.  There used to be a magic number in this area, I want to say 8ms.  Basically, anything slower than that was going to be visible and result in ghosting or a pixilated image.  I'm sure nowadays gamers say it needs to be 16ms or 20ms, but the plain old truth of the matter is that your eye cannot detect that, no matter how much you want to.  Native resolution used to be a big deal, but not anymore.  Contrast, as I said before, could be improved by using an LED type.  Color quality is pretty subjective and is something completely up to the individual.

                                         

                                        That all being said, I cannot tell you who makes the best gaming monitor.  My technical experience has only exposed me to screens no larger than 7" but that wouldn't preclude me from informing you of the above.  I will say one thing, however.  Today's marketplace is so fast moving and technology evolving at such a rapid rate that the best gaming monitor at 1:37PM CDT on 4/8/2010 could very well be different than the one at 5PM on 4/8/2010.

                                  • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                    ledmanmaker

                                    Good Morning, Brian.

                                    My name is Scott and I am currently teaching Industrial Technology/Art at a the high school level. I have been asked to develop a product design course and the first product that i wish to have the students work on is lighting. After researching products, materials, etc. I have decided that it would be most beneficial for many reasons to use the LED products.  My questions to you are: how would a fixture be wired to run the LED's off batteries as the power source? How many batteries for specific LED bulbs? I have also noticed a few pre-made fixtures that offer a 'remote' as well in order to operate the fixture. What do you know in regards to the type of remote and where to find them? My intent is to have students not only design the fixtures but to create 'functional' art at an affordable cost.

                                    I will look forward to your response.

                                    thanks for taking time out of your busy schedule to assist me with these questions.

                                    I am looking forward to starting the program as soon as possible.

                                    sincerely,

                                    Scott Smothers

                                     

                                    p.s. my school email address is:slsmoth@fresno.k12.ca.us

                                      • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                        ledmanmaker
                                        I am new to this site and was wondering how long on the average does it take to get a response?
                                        • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                          bkcoates

                                          Good morning Scott.  Again, I apologize for the delay.

                                           

                                          How would a fixture be wired to run the LED's off batteries as the power source?

                                           

                                          There are a couple ways to go about this.

                                          • The first is to use some standard power, high brightness LEDs formed in an array to output the desired light pattern; such as in a strip to mimic a fluorescent fixture or in a circle to mimic a light bulb.
                                            • The standard power LED (2-6 lumens output each) will draw 20mA, however, an array of them in parallel would increase current consumption dramatically.
                                            • A series array will be more current efficient, however voltage stacking may cause the need for a complex battery pack system
                                            • A series-parallel combination will likely be the best course of action for a battery powered light source, but the brightness will more consistent to that of a night light and would degrade rather quickly as the batteries drain.  A resistor inline with each parallel strand will be all that is needed to keep the LEDs for thermal runaway (drawing more current from a constant voltage source as the junction heats up during use).
                                            • A simple circuit could be 2 branches of the highest brightness 4 cool white LEDs you can find (8 LEDs in total). This would consume 40mA at 12.8V and yield approximately 20-60 lumens of total light.
                                          • The other option is to use high brightness or high power LEDs (60-120 lumens each).    A high power LED will draw 350mA (1W) or more.  This will make a battery powered fixture somewhat impractical due to the current draw.
                                          • For reference, the output of a general use 60W light bulb is around 600 lumens.

                                           

                                          How many batteries for specific LED bulbs?

                                           

                                          This would depend on your configuration.  A single 1.5V watch battery could power one of these for roughly 1 month before it is totally dead; however usable life is really only about 1-2 weeks at most.  But that is at a power level suitable only for indication, not illumination.  The above configuration would require 8 1.5V batteries (standard alkaline battery types) or less batteries if you used the more powerful lithium-ion type camera batteries.  I think those are available around 3.7V and have 1k mAh with the added bonus of being rechargeable.

                                           

                                          What do you know in regards to the type of remote and where to find them?

                                           

                                          Remotes will need to incorporate logic into the system to detect, decode and perform the instructions.  This is a complex arrangement involving either an RF transmitter and receiver or an IR (line of sight) transmitter/receiver pair and a simple microcontroller/FPGA that would need to be programmed to perform the desired functions.  I wouldn't recommend going this route unless the class was very technologically savvy or you had an embedded programming engineer available to you as a resource.  I would, instead, recommend using a simple switch, or even a 2 or 3 position switch that allows the user to chose between off and varying brightness levels.

                                           

                                          I hope this gets you started in the right direction.

                                        • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                          chrisadams

                                          Hi Brian

                                          I am a simulator visual engineer researching an eye limiting visual dome display and am considering the use of led displays. the properties are excellent except for the resolution, due to the  limitation of rgb smt size. I have found that Osram have developed a 1.6mm x 1.6mm smt rgb led giving a potential pixel width of 2mm, but have been unable to find any displays that use it?

                                          have you seen any example of these led's in use?

                                            • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                              chudson

                                              Hi Brian, I've been working on an LED lighting project for a while now. I've been working with LED's that typically have a 3.2V drop and a current usage of around 350mA. I have been using 50W high power resistors to drop the voltage and current to an acceptable level with a 12V power supply but this design isn't exactly efficient nor compact.

                                              I have looked into constant current driver designs utilising 2 transistors, a zener diode and several resistors. But I'm finding that the main transistor that doing most of the work is getting incredibly hot with just 1 LED running on it. I want to be able to guarantee that the final product will last a minimum of 5 years but doubt that this will be the case with this design. Is there any better designs for a constant current driver?

                                                • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                                  bkcoates

                                                  Christopher,

                                                   

                                                  There are many manufactures out there that are offering constant current LED drivers such as National Semi, TI and Toshiba.  Many of these drivers could be ideal for your project, but you are going to find that dealing with the heat effectively will be the means in which you guarantee your 5 year lifespan.  The LED that draws 350mA likely needs some heat sinking as well as whichever scheme you decide to use to create your constant current source.  Adding more LEDs only further complicates this.  Some of the steps you can take without going to a full blown metal fin heat sink is to use a metal core PCB and thermal past between the heat slug on the LED/transistor and the PCB.  Should you need to reduce heat further, you may be able to employ a solid state fan such as the one made by Nuventix.  Should this not be good enough still, then I am afraid you would have no choice but to integrate a larger metal heat sink of some design.  Generally, I would consider a high power lighting device "cool" if operated at 15-20 degrees Celsius warmer than ambient.

                                                • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                                  bkcoates

                                                  Chris,

                                                   

                                                  I have not seen any of these items in use in LED sign type applications.  The size for SMT RGB LEDs does create some problem in trying to reduce dot pitch.  Most sign manufactures still prefer to stick with through hole devices because of their relative durability when it comes to things like PCB flexure.  Through hole devices tend to also be brighter and have specific view angle properties that sign makers desire.  I am not trying to dissuade you from using the device in this manner, but only explaining why we haven't encountered more widespread use of SMT LEDs in LED signs.

                                                • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                                  JPVola
                                                  I want to generate low voltage (9-12V@500mA or more) pulses (10µs wide, 10ms time delay) to commute blue power LED (LUXEON star/O). Is it possible to obtain SPICE model of these LED (or equivalent, with Total Included Angle 25  degree max) ?

                                                  Thanks.

                                                    • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                                      bkcoates
                                                      Most LED manufacturers do not create SPICE models for their products.  Although there are a few that do.  I am not certain that Phillips offers SPICE models to their customers.  These SPICE models would be electric models.  I've not seen a SPICE model that would include light dispersion, luminous flux etc...  Most optical engineers use a different simulation software when it comes do device output such as Breault ASAP, Code V etc...  I hope this helps get you in the right direction.
                                                    • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                                      nikro

                                                      Пожалуйста помогите купить такой дисплей. Кто изготовитель? Спасибо!

                                                      • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                                        hawghunter
                                                        dear brian I am trying to under stand something about neon led lights.. i am starting to work on a project to create a bright neon green light that is dc powerd and can be used on or underwater. I have obtained three small led lights. they can be ran from a 9 volt battery but they dont seem to put off the brightness that i am looking for. I am looking to put quite a bright neon green cast on the water. if you can help me to understand about neon leds better and for what i need to do i would greatly appreaciate it..........................thanks frankgriffin........hawghunter_15@yahoo.com
                                                          • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                                            bkcoates

                                                            Frank,

                                                             

                                                            Trying to replace other technologies with LED lighting is still quite difficult.  Even the brightest LED still come up lacking when trying to compete against a light bulb or neon lights.  An array of high bright/power LEDs will likely be needed to meet this application needs.  The other point is color matching.  LEDs emit specific monochromatic colors.  Trying to match one of those colors to that of a neon light may prove to be difficult.  The best suggestion I can give is to try an array of 525nm green LEDs that operate from a constant current source of 125mA or greater.  As you may see in some previous posts, this requires some heat management techniques that you may not have had to do prior.

                                                          • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                                            hashir

                                                            Hi Brian,

                                                             

                                                            I am currently doing a project in which I will have to create a virtual reality environment on a micro display be it OLED or LCD/TFT display for a psychology based research I have been looking at OLED displays from Farnell for example  DD-9664FC-2ADD-9664FC-2A but I wonder whether these displays can play video footage I was also looking at TFT displays like LQ035Q3DW02 in case these OLEDs cannot play video and all of these come with a serial or parallel interface What I need is to control these displays using VGA/DVI port of the PC itself Would I be able to achieve this using an LCD/OLED driving circuit,with which I will be able to interface between the VGA port and the parallel port of the display If so would parallel or serial interface be easier Are there any pages/sources that can give me some information about the driving circuit too

                                                             

                                                            Thanks,

                                                            Hashir

                                                              • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                                                bkcoates

                                                                Hashir,

                                                                 

                                                                The  DD-9664FC-2ADD-9664FC-2A would be able to play video footage should you requite it Any TFT would be ale to do the same The trick is in using a proper interface The parallel/serial methods need an intermediary decoding"station There are a variety of manufacturers out there that develop decoder boards for TFT displays These decoder boards usually translate a PAL or NTSC(typical outputs for AV equipment such as a DVD player signal to either a parallel or serial interface People that build these types of decoder boards often work directly with a specific manufacture to optimize connectivity timing etc Your best bet in finiding the best method of decoding is to ask the manufacturer of the device for decoder board recommendations

                                                                 

                                                                If you want to build the decoding structure yourself, as I interpret from your question regarding parallel and serial interfacing, then the task becomes a little more difficult.  However, the decision to work with a parallel or serial interface depends solely on your experience, or you programmers experience.  Parallel is faster and more complicated (multiple instructions at one time), serial is slower, but easier to program (one task at a time).

                                                              • Where can I get small 7-segment LCD displays?
                                                                wos

                                                                I want to build (prototypes first, then manufacture) a gadget that has a small seven-segment display, say 7 or 8 digits, with digits about 0.2 inch high.

                                                                 

                                                                Do you know of any off-the-shelf source for this sort of thing? I've found several suppliers that sell big displays (1-inch digits), but nothing tiny. I could even use a pair of 4-digit digital watch displays for a prototype, but again, I have no idea where to find them.

                                                                 

                                                                For a prototype, all I need is digits. In production, I'd want to commission a custom display that has some symbols in place of some of the digits. Any suggestions on where I should go for that?

                                                                 

                                                                What sort of costs should I expect for production use, and what sort of NRE for tooling/setup? Should I be looking at different manufacturing processes/suppliers if I want 200 displays for a pilot run vs. 20,000 for a production run?

                                                                 

                                                                Finally, I don't know much about LCDs, but I gather there are several types. My biggest drivers are price and low power. The display doesn't change frequently (minutes, not seconds). Readability is not a big driver (gray-on-gray is OK), and backlighting is not in the picture.

                                                                  • Re: Where can I get small 7-segment LCD displays?
                                                                    bkcoates

                                                                    Olin,

                                                                     

                                                                    We make a variety of seven segment LED displays.  We have a product that is 0.33 inches tall (the digit itself is 0.22 inches); LDQ-M2212RI for example.  This display has 4 digits and a negative sign out front.  This should work well for prototypes.

                                                                     

                                                                    NRE for an 8 digit device can get fairly costly.  Also in the equation could be feasibility. The smaller you shrink an LED display the more you risk having bleeding from one segment to another due to very thin walls inside the plastic reflector.  I would not be surprised if tooling for this would be in the area of about $8000 USD.  Unit cost is fairly tricky to gauge without a design but you might be able to expect an LED display to cost around $3 USD or more per piece.  Lumex allows its customers to build prototypes (first article samples 10-20ish) a pilot production run (500ish pieces) but then usually the minimum order requirement after that is 1000 pieces.

                                                                     

                                                                    LCD displays are generally more cost effective; around 1200-2000 USD of NRE and piece prices in the region of under $3USD without any logic included.  The LCD drivers are fairly inexpensive as well, but LCD driver IC lead times are currently at an all time high - beyond 26 weeks in some cases!  Working with an LCD driver is pretty much the same as working with an LED driver.  So, the main difference between the 2 technologies comes down to operating temperature range and the need for low light readability (in the case of not using an LED backlight).  If you can settle for a smaller range in both cases, an LCD technology might be just what you need.

                                                                     

                                                                    Please note that my costs above are estimations and are made mostly for comparison's sake.  The actual quote will inevitably vary with the design specifications.

                                                                  • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                                                    e044730

                                                                    Why doesn't there seem to be many LCD displays with a SPI interface?

                                                                      • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                                                        bkcoates

                                                                        Kevin,

                                                                         

                                                                        I do not know this answer in its entirety, but I can speculate in a generalized way that seems to make sense.  SPI interfaces generally send/receive data much slower than a 4/8 bit parallel system. More complex LCD display systems, such as graphic or full color TFT modules, need the information display to happen so quick as to support a realtime refresh rate (such as 75Hz) so that the image seems fluid.  Most of the SPI interfaces available cannot support this data rate.  So, the industry generally accepted a parallel interface to be the norm across all LCD display technologies over time.  This, of course, doesn't mean that SPI or I2C interfaces do not exist, they are just far more rare and more costly to manufacture.

                                                                      • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                                                        e044730

                                                                        Brian,

                                                                        I am looking for surface mount LEDs that operate at 200deg C.  Do you know of any?

                                                                         

                                                                        Kevin

                                                                          • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                                                            bkcoates

                                                                            Kevin,

                                                                             

                                                                            e044730 wrote:

                                                                             

                                                                            Brian,

                                                                            I am looking for surface mount LEDs that operate at 200deg C.  Do you know of any?

                                                                             

                                                                            Kevin

                                                                            The survivable junction temperature for an LED die is 125deg C.  Anything beyond this temperature starts to delaminate the junction and the LED will cease to function as intended.  It is extremely unlikely for a solution to be found unless the technology of LED lighting changes.

                                                                          • Upgrading options from HPS or PMH to LED technology
                                                                            sbauman
                                                                            Hello Brian,

                                                                            I am wondering if you can help suggest a LED lighting alternative to the one I already have in our facility. I currently have 8X GE 480 Watt lighting fixtures we use for our main lighting, please see spec below and attached:

                                                                            GE 480Volts, 1.1 amps
                                                                            lampe watts 4000 LU 60 htz 480 watts
                                                                            P400BG25480V
                                                                            118C6180G25

                                                                            The reason I ask is we are desperately trying to reduce the devices
                                                                            that generate heat at the observatory as well as reduce our energy
                                                                            consumption in all devices as well.

                                                                            I know we could lower the wattage but this will
                                                                            will reduce the light levels in the area. I have considered a 750w pulse
                                                                            metal halide in the PF1000.
                                                                            The energy consumed by the 750w is appox 85 watts compared to 106w with
                                                                            the 1000w hps. The light levels for the 750w is appox 68000 lumens vs.
                                                                            130000 lumens for the hps. But I would really like to reduce the heat produced and wattage used by converting to LED technology.

                                                                            Please let me know if you have any products that you would recommend for replacement lighting fixtures with LED technology?
                                                                            Thank you for your time.

                                                                            Steve
                                                                            • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                                                              shashidharks

                                                                              dear sir,

                                                                               

                                                                              I required LED leghting design, LED constant current controll circuit

                                                                              Please guide me

                                                                              • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                                                                schreck

                                                                                Brian,

                                                                                 

                                                                                I am putting a circuit together of 4-6 leds I'd like to use 4 but can use 6 that runs off of 120v ac and has a light dependent resistor... I am new to electrical and I am trying to fit this inside of something that is 1/8" to 1/4" thick and 6" long 4" wide...I have to make this as cheap as I can too... If you have any suggestions or ideas that will be great..

                                                                                  • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                                                                    bkcoates

                                                                                    Robert,

                                                                                     

                                                                                    Most LEDs run in the range of 2-2.5 volts.  You need to modify the 120V AC power before you let it get to the LEDs.  There are a few ways you can do this:

                                                                                     

                                                                                    1. Step down transformer: a simple low power 10:1 (120 down to 12) step down should do the trick.  This could get bulky and bulky tends to go with expensive with transformers.  But this is the simplest method you could employ.   120 -> step dpwn -> photo resistor -> LEDs in series.  LEDs are a DC device, but at this voltage level, getting reverse biased for the negative portion of the signal will likely not be enough to damage them.  The will be off during this negative cycle.

                                                                                     

                                                                                    2. Modification to the above: 120V -> step down -> half wave rectification -> photo-resistor -> LEDs in series.

                                                                                     

                                                                                    3. This would be the full blown AC to DC converter found in most 12 and 5V power supplies.  Either you find a pre-made power supply or you have to make your own.  The simplest way is to do #2 this way: 120V -> step down -> full wave rectification -> filter capacitors -> photo-resistor -> LEDs in parallel or series (depending on the voltage level you go down to).  This would very well be the costliest option, but you would get a fairly smooth DC voltage near the target voltage level.

                                                                                     

                                                                                    Best regards,

                                                                                    Brian

                                                                                  • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                                                                    1728TERRIMILL

                                                                                    Brian,

                                                                                    I am trying to find the correct LEDs to use on a boat for the anchor light. It has to be seen at 360 degrees and at a 1 mile distance. Since boats need it to be on all night saving 12 volt power is a big plus. Do I need 4 each facing a different direction? 12 volt is the power on board.

                                                                                    Thank you

                                                                                    Jim

                                                                                      • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                                                                        bkcoates

                                                                                        Jim,

                                                                                         

                                                                                        The LEDs that you would want to use in an application like this have a beam angle of about 120-150 degrees.  That means that you will be about half of the original brightness when viewing the LED 120 degrees of axis.  That said, your application is one of safety and identification and needs to be seen from a great distance.  Having 4 LEDs each facing 90 degrees from the next would be a pretty good layout, but I am not sure if you get an optimum output.  If you use 5 LEDs equally space, you could get a spread of 72 degrees.  So there would be better overlap and ensure you had 360 degree visibility from long distances at night.

                                                                                         

                                                                                        Best regards.

                                                                                        Brian

                                                                                      • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                                                                        Jacenty

                                                                                        Dear Sirs

                                                                                         

                                                                                        I would like to use AM OLED colour display 240x320-2.8" in a new design, like for instance Densintron C0283QGLD-T. As far as I now, the said displays are not in production at present. My question is whether thise displays will be available in future or if they are to be replaced with any other similar AM OLED display. What are perspectives for availability of the AM OLED colour displays?

                                                                                         

                                                                                        Awaiting your reply

                                                                                         

                                                                                        Kind regards

                                                                                         

                                                                                        Jacek Barański

                                                                                          • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                                                                            bkcoates

                                                                                            Jacek,

                                                                                             

                                                                                            AM OLED modules are still quite an immature technology.  They are more widely available today than they were even a year ago, but there is a lot of work still to be done to improve the lifetime.  Certain colors on the OLED still get under 10k hours.  It does not surprise me that you are having trouble getting some for your design.  There are some manufacturers out there that may be able to help you, but you need to be aware of the risks to make sure that it is sensible to fit one into your design, especially when TFT alternatives at that size are so cost effective in comparison.

                                                                                             

                                                                                            I hope this answers your questions.

                                                                                             

                                                                                            Best regards,

                                                                                            Brian

                                                                                          • LED mounting, directing the beam
                                                                                            vsuontam

                                                                                            Hi,

                                                                                             

                                                                                            I am looking for a way to mount near infra red power LEDs into surfaces such a way that they could directed after the mounting. The LED we are looking to use:

                                                                                            http://www.epigap-berlin.com/uploads/tx_mvmdprodukte/ELJ-870-629_03.pdf

                                                                                             

                                                                                            We are going to install these LEDs into outside environment as marking LEDs for near infra red cameras, one LED every 1 meter or so.

                                                                                             

                                                                                            The viewing angle of such led is quite small (approx 17 deg), and we would need to find a robust way to adjust the direction of the lens (left, right, up, down) up to 60 degrees from the mounting position to all directions. Is there a ready made "collar" that cold be used? Any ideas where to look for such LED mounting? Or any other way to direct the beam?

                                                                                             

                                                                                            Thanks in advance,

                                                                                             

                                                                                            Vesa

                                                                                            • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                                                                              VNUORT

                                                                                              I recently bought a 900 lm flashlight Ultrafire WF-502B from Deal Extreme Hong Kong. It contains SSC P7 led and Trustfire TR18650 2500mAh 3,7V battery. At first the light was very bright, but after being on for a couple of minutes the light intensity was reduced remarkably without any visible reason. Later I noticed that only one of the four led elements on the chip was on and the other three were off. When I made a claim to DE they asked me to find out( from sites which deal these kind of things) what was the possible cause (or remedy) for the fault before they would do any further actions. My opinion is that the led chip is broken and the only possible cure is to replace it. Possibly the reason for breakage is overheating of the chip because of poor heat dissipation? What is your opinion?

                                                                                               

                                                                                              regards

                                                                                               

                                                                                              Veikko Nuortio

                                                                                              • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                                                                                Eclipze

                                                                                                Hi Brian,

                                                                                                 

                                                                                                I'd appreciate your comments regarding the measurement of brightness.  I have gone through the calculations to convert mcd / degrees to lumens etc... however the calculations are not entirely useful given the projection profile of the LEDs.  I would really like to measure the mcd of the actual light source, rather than rely on calculation estimates and claimed outputs on datasheets. 

                                                                                                 

                                                                                                I haven't seen equipment that will measure candela, only lux.

                                                                                                 

                                                                                                Given...E = I / d²E = the illuminance, in lux.I = luminous intensity, in Candela.

                                                                                                d = distance, in meters.

                                                                                                 

                                                                                                ...measuring a light source from 1 meter away with a lux meter should give mcd.  However in practice I have had reason to question the accuracy.  This may be because I was attempting to measure the brightness of an array of red LEDs, and the pure wavelength is not suited the sensitivity of the lux meter sensor.  The meter may designed for daylight use.

                                                                                                 

                                                                                                Could you offer any advise on how to measure the mcd of an LED source?  Equipment / Method?

                                                                                                 

                                                                                                Cheers,
                                                                                                Tony

                                                                                                  • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                                                                                    bkcoates

                                                                                                    Tony,

                                                                                                     

                                                                                                    Most of the equipment I am familiar with is made in Taiwan.  However, I have run into a San Diego based company that makes some of the same type of equipment.  They can be found at http://www.gamma-sci.com/products/radOMA-LED.html.  The specific machine I linked to is purported to measure Luminous Intensity in candelas.  There is another company based out of LA whose equipment I do utilize as well, http://www.photoresearch.com/.  If the equipment cost is too high to absorb, I'm sure both companies offer or can refer you to third parties that do that sort of testing with their equipment.

                                                                                                     

                                                                                                    Best regards,

                                                                                                    Brian

                                                                                                      • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                                                                                        Eclipze

                                                                                                        Thanks Brian!  I don't need a quote to tell me that those pieces of test equipment won't fit within my budget.

                                                                                                         

                                                                                                        Do you have any ideas on a more rudimentary method?  I have had thoughts of using LEDs of the same wavelength with known brightness bin as a reference source.  Then comparing a reading using a Lux meter and calculating by ratio for the unknown.  I would hope that if I'm dealing with relative similar brightness levels, I could possibly achieve a realistic measurement.

                                                                                                         

                                                                                                        Do you have any other thoughts?

                                                                                                         

                                                                                                        Cheers,
                                                                                                        Tony

                                                                                                    • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                                                                                      jcdammeyer

                                                                                                      Hi Brian,

                                                                                                       

                                                                                                      I've done a number of LED projects now all with through hole LEDs.  White LEDs for the suspension cable lights on the lions gate bridge in Vancouver.  RGB (plus white) LEDs for the Winter Olympic Rings in Vancouver and at the YVR airport.  We used very narrow angle LEDs for the rings at the airport to avoid disturbing the flights at the airport.  Off axis the rings were not visible at night.

                                                                                                       

                                                                                                      Since they were through hole LEDs we wave soldered them.  Rather conventional with large copper areas for heat sinks.  Is there an app note for XPCWHT-L1-0000-007E7-STAR.XPCWHT-L1-0000-007E7-STAR. type high power LEDs.  How to mount to PC boards or to Heatsinks?

                                                                                                       

                                                                                                      Thanks

                                                                                                      John

                                                                                                        • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                                                                                          bkcoates

                                                                                                          John,

                                                                                                           

                                                                                                          I am unaware of the specific app notes available from most of my competitors, but mounting the metal core PCB to a heat sink is a critical item to ensure the longest lifetime and best performance from your LED and optics.  I wish I can give a straightforward answer, but applications vary.  The best advice that I can give is that the contact between the metal core PCB and the heatsink needs to be as large as teh surface area will allow.  This is generally best acheived by coupling the PCB and heatsink with a thermal grease/paste.  Mechanically, a bolt option would be ideal to maintain the integrity of the connection.

                                                                                                           

                                                                                                          I hope this points you in the proper direction.

                                                                                                           

                                                                                                          Brian

                                                                                                        • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                                                                                          doubleflatted8

                                                                                                          Hello Brian,

                                                                                                           

                                                                                                          I am a senior EE starting on my senior design project. Our group is going to design a touch screen Rubik's cube, and I am handling the TS input and LCD output end of the design. Obviously, I am very new to LCDs and how they are controlled. I am  beginning to get some experience in RGB with one of my other courses, so I think RGB is the way I want to handle this project. I am simply looking for a general direction to begin a more focused research/design of my components. I am currently looking at the LCT-H320240M35WTLCT-H320240M35WT to use for the 6 TS LCDs,  and I have a few questions you can help with me hopefully.

                                                                                                           

                                                                                                          1. This part appears to be designed for RGB digital input. What I'm wondering is what are the benefits of using RGB instead of the other types of data transfer, and do you think RGB is the way to go for this type of application?

                                                                                                           

                                                                                                          2. Can you give me an idea of the general transfer of data? My general block progression is TS input -> TS ADC -> microprocessor -> RGB DAC -> LCDs

                                                                                                           

                                                                                                          3. Obviously, since there are 6 TS LCDs, thats a lot of data to be handled and processed. My initial idea for input signals is to implement some control logic to limit the ADC to only receive input from one touch screen at a time, similar to how you can only turn one side of a rubik's cube at a given time. But as far as output to the 6 LCDs, I'm not sure where to begin. Do you have any suggestions on how to control 6 LCDs at the same time, each of them displaying data that is dependent on each other?

                                                                                                           

                                                                                                          4. Will one microprocessor be enough or due to the amount of data being handled, would I need several?

                                                                                                           

                                                                                                          5. Finally, the data sheet for the LCT-H320240M35WTLCT-H320240M35WT is fairly lean in operation instruction, and while I've begun studying the controller embedded in this part, I was wondering if there is a more comphrehensive look at the operation of this device. I am going to purchase one soon to start becoming acclamated with how the device works. Below in the data sheet...

                                                                                                           

                                                                                                          http://www.lumex.com/specs/LCT-H320240M35W.pdf

                                                                                                           

                                                                                                          Thank you so much for your time and consideration. I cannot express to you how valuable any help or advice you can give me will be.

                                                                                                           

                                                                                                          Tony

                                                                                                          • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                                                                                            watchmefly

                                                                                                            Brian,

                                                                                                            I currently have a sanyo tv with a broken lcd screen, I was wondering if you knew a place to purchase a replacement. Searched the web and couldn't find anywhere that sold it, even emailed sanyo and they wouldn't even contact me back. Any help would be greatly appreciated. Thanks in advance

                                                                                                            Tyler

                                                                                                            • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                                                                                              DAB

                                                                                                              Hi Brian,

                                                                                                               

                                                                                                              I am building an LED light ring for Macro photography.  I want to be able to adjust the brightness of each LED individually, but control three separate banks on and off with a single switch/command.  Is there an easy way to do this with a LED controller?

                                                                                                              Also, if you use PWM to adjust the brightness, what are the modulation frequencies?  I worry that PWM could produce undesired artifacts in the photos.

                                                                                                              Does PWM change the spectral output of the LED's or are they more spectrally consistent with a constant current and voltage?

                                                                                                              Thanks,

                                                                                                              DAB

                                                                                                              • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                                                                                                xopher21

                                                                                                                Hey Brian! 

                                                                                                                 

                                                                                                                I came across this fabulous LED room while I was researching on various clubs as I am interested in opening a couple here in the United States.   I was wondering how much (ball park) would this cost for the product and installation.  The following link is a youtube video of the club I wish to duplicate more or less.  Also, do you know a good company that is capable of this?

                                                                                                                 

                                                                                                                http://www.youtube.com/watch?v=V9AySS3Ff2Y

                                                                                                                 

                                                                                                                Please refer back to me at your earliest convenience.  Thank you!

                                                                                                                • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                                                                                                  William Cookson

                                                                                                                  Dear Brian:

                                                                                                                   

                                                                                                                      I have recently received an old LG LCD display (Model L226WTQ-SF) that doesn't have power to the controller module (the capacitors look like they have failed) and I was wondering whether you could suggest what quality or brand of capacitors would be best to replace the dead ones in the power unit?  I want something that will last longer than the original caps (roughly four years) to keep the monitor going until another piece fails on it.  Please pardon me as this is my first post to Element 14 and I wasn't sure whether I should ask you or the Caps expert.  Any help would be appreciated.

                                                                                                                   

                                                                                                                  -WJCTechy

                                                                                                                  • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                                                                                                    shivang ghetia

                                                                                                                    hey,i have done 8x8 LED matrix but when i go for moving a string on matrix,one row goes very low light emmiting condition

                                                                                                                    and when i give derect ground to this row,i enlightens very efficiently.

                                                                                                                    can you tell me what may be the reason?

                                                                                                                    • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                                                                                                      jeffjohnvol

                                                                                                                      Hi Brian.  I''m working on a mini-sumobot and plan on driving 5  IR LEDs at 38Khz from a single pwm output of my Arduino Pro.  Can you suggest a good circuilt that allows me to vary the intensity of the LEDs at 38KHz to fine tune my distance measurements?  I'm not worried about the 38Hhz receiver module, as I have that piece buttoned up solid.

                                                                                                                       

                                                                                                                      Thanks.

                                                                                                                      Jeff

                                                                                                                      • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                                                                                                        wos

                                                                                                                        A while back, I asked about small LCD displays, and now I'm back working on that. Can you suggest any vendors to look at for (A) a few stock 7-segment LCD 8-digit displays  for prototyping and (B) pilot production quantities of a small (4mm  digit height) custom display with five or six digits and a few special  symbols. Google coughs up a lot of hits, but it's hard to tell what's what, and it's pretty clear that the list isn't comprehensive.  I figure someone must make all those little displays in throwaway  solar-powered calculators (or the calculators themselves--those would be  fine manufacturers for the product I'm looking at).

                                                                                                                        • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                                                                                                          GeneSinacori

                                                                                                                          I am building a test box and need to light some panel mount LEDs.  I have a 9 volt power supply.  I can only find 6 volt and 12 volt LEDs.  Will either of these work with a 9 volt power supply?  Will I need current limiting resistors?

                                                                                                                          • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                                                                                                            newj1952

                                                                                                                            I just bought a Dialight 137-8836-0931-552137-8836-0931-552 front panel power indicator and it did not come with a neon bulb.  I've looked at the data sheets and I can't figure out what kind of bulb fits in the power indicator housing.  I have installed it on a guitar amplifier and it is connected across the 120 VAC of the input of the power transformer.  What kind of bulb do I need to order that will work in this configuration?  Where can I get such as bulb?

                                                                                                                             

                                                                                                                            Jim

                                                                                                                            • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                                                                                                              Johannes*

                                                                                                                              Hi Brian,

                                                                                                                               

                                                                                                                              I'm looking for a ultra-low power low voltage LCD segment display. The segment display will be used in a thermometer, so two digits plus the degree sign "°" would be optimal.

                                                                                                                              The operating temperature will vary between -10°C and 65°C; character height should be about 1 cm.

                                                                                                                               

                                                                                                                              Do you know where to get such a small seven segment display? I already stumbled upon the bistable LCDs from Lumex

                                                                                                                              (http://www.lumex.com/images/Lumex_Bi-Stable_LCDtechnology.pdf)

                                                                                                                              an ultra low power display from ParasitiX

                                                                                                                              (http://www.linkedin.com/company/parasitx-llc/low-power-3-digit-lcd-display-30726/product).

                                                                                                                               

                                                                                                                              Actually the one from Parasitx looks pretty much what I had in mind. However I wasn't able to find in a store and maybe there is even something "better" out there you know of.

                                                                                                                               

                                                                                                                              Thanks in advance

                                                                                                                               

                                                                                                                              Johannes

                                                                                                                              • Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
                                                                                                                                IMTAPASPANI

                                                                                                                                I want to set up a LED lighting solution industry in India, Please tell me how to do techonlogy for this.

                                                                                                                                 

                                                                                                                                Thanks & Regards

                                                                                                                                Tapas

                                                                                                                                 

                                                                                                                                 

                                                                                                                                This thread has been closed to new questions.

                                                                                                                                However, we welcome you to Post Your Button about Lighting in the element14 Community Lighting group. You'll find many fellow members and experts who have just the answer you're looking to find! 

                                                                                                                                 

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