Ask A Scientist© General Science Archive

name        Edward
status      student
age         9

Question -  I am doing a demonstration of the fact that black and
darker colors absorb more heat than white and lighter colors. I am using
felt in colors of the rainbow (ROYGBIV). I wanted to know why, at the
molecular level, this happens. From what I have read it seems that
colors get warmer as you go from longer to shorter wavelengths because the
longer wavelengths are closer to the infrared wavelength and so can produce
or transmit(?) more heat than the shorter wavelengths. So, a red cloth
 will be cooler than a violet cloth when shined on with a light for a
given amount of time because the red cloth is reflecting the red
wavelength--and absorbing all the other ones--which gives off more heat
 than the violet cloth which reflects violet (a shorter wavelength which
is cooler). Is this accurate? If it isn't what's the real answer? Thank
you for replying ASAP. Edward
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Edward,

The simple answer to your question is that lighter colors have a greater
albedo...that is, they reflect more light.  Darker colors absorb
comparatively more light.  Since light is energy, an absorption would
increase a materials temperature.  Note that an object appears white if it
reflects all colors, black if it absorbs all colors.  Naturally there are
gradients of color and therefore gradients of absorption.  So, too, the type
of material will affect its relative heating.  For a given material,
however, this describes in simple terms the phenomenon you are seeing.

Thanks for using NEWTON!
Dr. Rupnik
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It's true that red and orange are regarded as warmer colors than blue
and violet, but this describes the way people feel when they look at
colors, and it has nothing to do with the abilities of different colors
to warm things up.  Actually a blue photon contains more energy than a
red one, and so if totally absorbed it would be converted into more heat.

In your demonstration, the only thing that matters is how much light is
absorbed, how much is reflected, and how much is radiated away.  The
darker the color, the less visible light it is reflecting and the more
it is absorbing.  The absorbed light is converted to heat.

There is a lot of missing information here.  Sunlight contains a wide
range of "colors" not all of which you can see.  There could be two
identical looking pieces of felt one of which absorbs infrared
radiation,the other of which reflects it.  The absorber would get
warmer.

Tim Mooney
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