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I did this work in early October when I had some free time on the weekend.  As a reminder, I was interested in how different colors of glow sticks spend their energy.  I know, for example, that blue is an energetic color of light, and that red is a less energetic color of light.  For a light source, giving off red visible light means that energy is being given off in small packets.  Its like spending $100 just pennies at a time. 


So I made a simple circuit just using a photoresistor inside a wooden box.  I used an arduino to capture the readings and sent it to a Xively account, and later downloaded that information and plotted it (thanks Peter Oakes!).  The Xively aspect of things was cool because I could see my experiment from anywhere in the world (even if I was only in the next room).  I was hoping for a gspread library so I could use a Google Doc, but I think that will have to wait.


At any rate, my results are below:




As you can see, Green and Orange behaved very similarly.  White, however, was always dim.  On all accounts, I was shocked by how quickly they faded.  I didn't expect it to be quite so exponential.  The X-axis is in seconds, which means that in a matter of minutes, the light being given off is really diminishing.  Green and orange have a sizeable difference in energy, so I was also surprised to see that they behaved so similarly.  I, do however, know that the green color is easy to make with luminescent chemicals.  Producing other colors often involves fluorescence.  That is something with high energy emits light, which gets absorbed by something else and re-emitted as lower energy light.  I think that might be the case here.  Still I was surprised to see that this didn't lead to much dimming.


White should be a collection of a lot of colors, but not of lot of things give off white light as part of luminescence, so there is probably a lot of muting and filtering just to get white.  In other words, it doesn't work great, and don't take it camping. 


All in all, I am pleased with how this went.  I am not done, not by a long shot.  I wasn't able to make my light detector (lux) work very easily with the xively account, so I had to settle for the photoresistor.  I will repeat this soon with the Lux sensor and will play with the positioning of the glow sticks as well.


Thanks, for all of the suggestions to make this work.  If you can see anything else that is interesting please let me know.  My goal would be to connect this to kinetics for a general chemistry class.


Lightsticks and Lux

Posted by mikedavis Oct 2, 2014

I am doing it.  This weekend!  I am done talking about it.  This is the weekend!


For years I have been imploring teachers, students, and parents to expand their mindset when it comes to the science fair.  I see a lot of


  • Which battery lasts the longest?
  • Which light is the best for plants?
  • Which diaper is the most absorbant?
  • Which music is makes me the calmest?


All of these are not without merit.  They teach process and you might get a good graph out of it.  At the end of the project, however, people haven't really changed their battery purchasing habits, or diaper habits, or gardening output.  That is, they are a project for the sake of a project.  In this case they are graded and mandatory.  I think, through open source electronics like the kind this network seems to love, there is a chance to do more engaging work.


For years, I have been curious about the lasting power of glow sticks.  I know that, as a chemical reaction, they glow dimmer and last longer when they are cold.  I know as a consumer that they come in a number of colors.  I am curious, as a scientist, if their light output changes with their color.  So that is my question.  If I was 25 years younger, it would be my science fair project.  Now it will be my classroom project.


Using the Arduino Uno and the Lux Sensor, I am going to be able to measure the light coming off one of these and measure its decay as a function of color.  I can also do it with temperature if the time and inspiration are there.  I am very excited, and this is the time. 


The only help I could use, and this is the best part of a community like this, is that I would like to be able to get my Arduino to send the information to a document like a spreadsheet, or a webapp like Xively.  Any advice there would be very helpful.


Stay tuned for results!