Which colors absorb more light energy?

Figure 1. A page with some color
strips under a table lamp. Click the
image to enlarge it to see the details.

We all know black objects absorb more light energy than white ones. What about red, green, blue, and any other colors? With an affordable infrared (IR) camera, this is very easy to figure out. (Update in 2015: There are now a few IR cameras that are priced under $300, such as FLIR ONE and SEEK THERMAL)

Use your word processor to draw and print some strips in any color you want on a page, as shown in Figure 1. Put the page under a table lamp (or sunlight) and let the light shine on it for 10 seconds. Then aim an IR camera at the paper. Figure 2 shows the results.

Figure 2. An IR image showing the
amount of light energy absorbed by
the color strips.

Obviously the black strip absorbed the most. But the red, blue, and green ones did not absorb much. Interestingly, the dark gray and purple ones seemed to have absorbed more energy than I would imagine.

I have to admit that I didn't know how other colors absorb light energy before doing this experiment. With an IR camera, you can easily check it out just on your own like what I did--for any color and any comparison.

If you have heard that Steve Chu, our Energy Secretary, has been serious about advising people to paint their roofs with light colors and Mayor Michael Bloomberg has agreed to answer the call in New York City, you may find this little experiment worth your while--you may pick a color that does not absorb a lot of energy yet it will be more colorful than white.

Updates in 2013: Links to my YouTube videos about this experiment:

• Under sunlight
• Under table lamp