Expert: Optics C - 3/6/2008

Question
I am in eighth grade and will try to understand even the most complicated of
answers. My question is: How do colors affect the rate of heat absorption?

Answer

Andy,
I'm not sure exactly how to interpret your question, but I will try.

Heat and light are two different things. Light is an electromagnetic wave and heat is kinetic energy of particles. Because light carries energy, it will heat up absorbing surfaces upon which it is incident. That is, light incident on a brick will cause the particles in the brick to vibrate. These vibrations are "heat."

The contribution of color is simple. Those objects that absorb light better heat up more. Darker colors absorb more light than brighter colors, so they will heat up more. The relative color of an object (red vs. green) is harder to generalize. If the light source is dominantly red, a green object will heat up faster than a red one (because the red light is absorbed by green and reflected by red). The opposite is also true.

Much confusion occurs over infrared light, which is invisible to the eye but can transmit energy. An example is standing near a bonfire; most of the heat you feel is caused by copious infrared light emitted by the fire. Early scientists assumed that anything causing heating was "heat" and anything they could see was "light," so infrared light was called "heat rays."

Best,
Curtis