Science Buddies: "Ask an Expert"

Hello. I am in 9th Grade and I had a question about the project, "Absorption of Radiant Energy by Different Colors". I changed it up a bit though. Instead of using all of the colors listed, i used black and white. Also, instead of using the sun, I used three different light bulbs, CFL, LED, and Incandescent light bulb. I put the lamp over the construction paper, take the temperature of the construction paper with the infrared thermometer before I turn it on, then I turn on the light bulb and wait 5 minutes. When 5 minutes pass, I turn off the light bulb and take the temperature of the paper. Then I subtract the before and after and I get the difference. Here are the results I got for trial 1.Trial One


Temperature in Room: 18 Degrees C

5 Minutes

Degrees Celsius


Incandescent 60 Watt

White Construction Paper

Before: 19.1

After: 20.6

Difference: 1.5


Black Construction Paper

Before: 19.4

After: 22.1

Difference: 2.7



LED: 60 Watts


White Construction Paper


Before: 19.1


After: 19.2

Difference: .1


Black Construction Paper


Before: 19.1

After: 19.3

Difference: .2


CFL: 60 Watt


White Construction Paper

Before: 19.3


After: 19.5

Difference: .2


Black Construction Paper

Before: 19.0


After: 19.4

Difference: .4


My question is how do I use the Stefan-Boltzmann law with this experiment. What do i plug in into the variable in the equation to get the amount of energy absorbed into the colors. Thanks! (This is due in 4 days!)

Scienceprojects101 - Sometimes it is very helpful to alter and expand an experiment for purposes of getting better results to support a hypothesis. I think, in this case, you are introducing too many variables (different light bulbs) and reducing the measured results (two colors instead of four). By using natural sunlight as your source, you are controlling the energy source very well. The simultaneous exposure of the four color test cards ensures that your measured results will be make analysis very straight forward. The introduction of three different light sources will introduce difficult variables, including spectral issues to complicate your result. Also, the sun will likely provide the greatest energy source compared to the other sources (greater differences in your readings). Note also that a 60 watt incandescent bulb will have very different output characteristics compared to the LED and CFL source. In fact, you may be comparing 60 watt energy equivalency when reading the specs on the other bulbs. Often, CFL and LED lights will only consume 5-15 watts while producing the same lumen intensity of the 60 watt incandescent bulb. This is how they market the energy advantages of these energy efficient bulbs. While this is all good for 'green energy' consumption, it will only confuse your experiment.

I suggest that you will get the best results by following the Science Buddies procedure or a similar experiment that controls your variables better.

Rick Marz

The problem is it is due soon and the sun is not out because it is currently winter (and snowing from where I am). So do you have any suggestions of what I can do in this short limit of time? Maybe I shouldn't talk about using CFL, just LED? etc. And would you happen to know how to use the Stefan Boltzmann Law with this? Thanks.

What you are measuring seems to have nothing to do with absorption of various colors. Black and white paper both absorb across the entire visible spectrum, as well as infrared and ultraviolet (though there may be peaks at some frequencies).

What your experiment is measuring is really a pretty good estimate of the entire energy output of those three types of lights, though it's quite difficult to control for the different distributions of light that these types of bulbs tend to put out. A "60W" LED bulb is actually not using or radiating the same amount of power as a 60W incandescent bulb (which, itself, may not be using 60W these days).

I would say that if you don't want to redo your experiment to actually measure absorption at different frequencies (using colored paper), your best bet would probably be to use a power meter to determine the actual power use of the 3 bulb types, and see if those correspond to the temperature changes you measured. That would be an interesting experiment all by itself.