The following is documentation of a student's experiment with color and heat absorption. We only know her as "Madeline" and here's the research that she posted on the bulletin board at Color Matters, January, 2000. If you have any resources (web sites, books. etc.) regarding color and heat absorption topic, please post it on the bulletin board.

Question
Does the amount of thermal energy (heat) produced by a colored fabric after 30 minutes of intense light relate to its position in the spectrum?

Hypothesis

When a color (colored fabric) absorbs light, it turns the light into thermal energy (heat). The more light a color absorbs, the more thermal energy it produces. Black fabric absorbs all colors of light and is therefore warmer than white fabric which reflects all colors. I predict that the colors of the spectrum appearing the darkest and most like black (violet, indigo, and forest green) will produce the most thermal energy. The other colors (red, orange, and yellow), will produce the least thermal energy because they appear lighter or more like white.


Materials

1. a thermometer (preferably an indoor/outdoor thermometer because they have the largest temperature range)
2. a 1’ x 1’ piece of heavy corrugated cardboard
3. tape
4. a clock, stopwatch, or timer
5. sunlight (If you’re short on sunlight, use a with a halogen floodlight, at least 100 watts. A halogen bulb is a good choice because it has a high light intensity and its light spectrum is very similar to sunlight.)
6. six 100% cotton T-shirts (or pieces of cloth) in red, orange, yellow, forest green, indigo, and violet


Procedure

A simple way to measure how much thermal energy a colored material produces is to measure the changes in its temperature:
1. Tape the thermometer in the center of the cardboard. Make sure the tape doesn’t cover the thermometer bulb.
2. Set the cardboard/thermometer indoors, out of direct sunlight.
3. Lay the red cloth over the cardboard/thermometer so it is touching the thermometer bulb.
4. Set the lamp so the bulb is 2 feet away from and perpendicular to the cardboard/cloth.
Turn the lamp on.
5. Position the cardboard/cloth so the thermometer bulb is in the center of the beam of light.
6. Wait 30 minutes, then record the temperature under the cloth.
7. Turn the light off and take the cloth off the cardboard.
8. Repeat steps 3 through 8 using each of the other colors of cloths. (Orange, yellow, forest green, indigo, violet.)
9. Repeat the experiment at least 6 times and calculate the average temperatures for each color.

Conclusion

My hypothesis is correct. The darker colors (forest green, indigo, violet) produced the most thermal energy after 30 minutes of intense light. The lighter colors (red, orange, yellow) produced smaller amounts of thermal energy. (The average recorded temperature (°F) for each of the colors is shown in Graph 1.) Interestingly, the temperatures of the fabrics fell in to two groups instead of increasing as the colors got closer to violet. The difference between the temperatures of the red, orange, and yellow fabric was minimal, only 10ths of a degree. The same thing was true for violet, indigo, and forest green fabric. However, the difference between the temperatures of the two groups was a little more than 3 degrees (Fahrenheit). In conclusion, even though violet, indigo, and forest green are generally referred to as "cool" colors, you will be warmer if you wear them! You may not be any warmer if you wear blue instead of green, or green instead of purple. Similarly, it won’t make a difference if you wear red instead of yellow, or yellow instead of orange, but on a hot day, wear one of the warm colors!


Bibliography

Gardner, Robert. Science Projects About Light. Springfield, New Jersey: Enslow Publishers, Inc., 1994, p. 92
Morton, J.L. Color Matters - Electromagneic Color - 1995-1999

About Light

There are many different kinds of light. The different kinds have different wavelengths. Ultraviolet light, for example, has a wavelength of 10-8 meters. Visible colors have a wavelength of about 10-6 meters, the diameter of a bacteria. Infrared light also has a wavelength of about 10-6 meters, but has a longer wavelength than the visible colors. The different colors of visible light have different wavelengths, but the wavelengths are very similar. Violet light has the shortest wavelength, is the coolest, and is closest to ultraviolet light. Red light has the longest wavelength, is the warmest, and is closest to infrared light. The other colors of visible light increase in wavelength and warmth as they get closer to red and infrared light. (For example, yellow light has a longer wavelength and is warmer than indigo light.)

When you shine white light (the light that includes all the visible colors) on a colored object, the object will appear to be the color of the light it reflects. All the other visible colors are absorbed. If the object reflects a warm color (red, orange, yellow) it will be cooler than an object which absorbs them. For example, if you shine light on a blue object, it will absorb the warm red light, and will be warmer than a red object which would reflect that light.

Results of Experiment (completed 8 times)

Cloth Color Red Orange Yellow Dk. Green Indigo Violet
Temperature( F) 76 77 76 80 81 78
78 76 77 76 82 78
76 77 78 83 79 82
76 79 77 80 81 84
78 78 76 86 83 82
78 75 78 81 82 80
78 78 79 79 78 84

77 77 77 81 81 80 Standard Deviation 0.991031 1.246423 1.035098 2.915476 1.642081 2.390457
Average Temp. ( F) 77.13 77.13 77.25 80.75 80.88 81