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

nlarson PremierFarnell

This thread has been closed to new questions.

However, we welcome you to Post Your Question about Communications 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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Please feel free to browse the achive of past member questions and Brian's answers below!

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

    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

  • 2. Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
    bkcoates e14 Expert

    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.

  • 3. Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
    cropcircles Level 1

    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/

  • 4. Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
    bkcoates e14 Expert

    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.

  • 5. Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
    cropcircles Level 1

    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/

  • 6. Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
    bkcoates e14 Expert

    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.

  • 7. Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
    cropcircles Level 1
    Thanks Brian for the feedback. It is fascinating how the technology is so rapidly growing and evolving. If you don't mind can I quote your response over at Neowin. 
  • 8. Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
    ledmanmaker Level 1

    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

  • 9. Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
    ledmanmaker Level 1
    I am new to this site and was wondering how long on the average does it take to get a response?
  • 10. Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
    bkcoates e14 Expert

    Scott,

     

    My apologies.  You have asked a rather lengthy question and I would like to formulate the best, most accurate answer that I can.  I try to reply to most messages right away.  Please allow me a few more hours to get back to you.

  • 11. Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
    ledmanmaker Level 1

    didn't mean to sound pushy, Brian.  My concern here is that once we get some money to spend at our school site you better spend quickly!

    I will look forward to hearing from you when you get a chance.

    scott

  • 12. Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
    bkcoates e14 Expert

    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.

  • 13. Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
    chrisadams Level 1

    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?

  • 14. Re: Have a question about LEDs or LCDs? Ask the expert, Brian!
    chudson Level 1

    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?

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