Re: Heat Absorbtion of Colors

Dear Lisa,

Your question is very interesting actually. Have you ever wondered why
people prefer to wear light colours in summer
instead?
Of dark colours? You have certainly already noticed that when you wear a
black T-shirt when it's sunny, you feel very hot.
Why so then?

In fact, when light is absorbed by matter, part of its energy may happen as
heat, that is, as like more vehement vibrations
of the constituent atoms or molecules.

If an object reflects the whole of the incident light without 
discrimination
it is called "white", while if it is so constituted that is absorbs all the 
light, it is designated black. Neither
100% absorption nor 100% reflectance are
attainable in practice, but there is an infinity of gradations between 
black
and white through grey in objects, which are
non-selective in their reflectance.

As you may know, the colours our eyes can see are vibrations that have
wavelengths are between 380 and 770 nanometers.
Einstein and Planck have worked a long time on light properties, and they
have found out the equation E=hU, where E is the
energy in Joules, H the Planck's constant and U (grecque letter nu) the
frequency in Hertz (Hz or s-1). Another equation is
also useful, c=lamdaU, where c is the speed of light, lamda the wavelength
and U the former frequency therefore
U=C/lambda.  I will show you in a minute that the equations are very 
helpful
to answer your question.

If an object, for example your T-shirt, absorbs most of the short 
wavelength
(therefore high frequency) part of the light (blue and green) and reflects 
the longer wavelengths (therefore low
frequency) only, it is seen as red or orange.  In the
other hand, if you wear a green t-shirt, it will absorb the long 
wavelengths
(red) and reflects the shorter wavelength end
of the spectrum. So while one associates red with warm sensations, and as
green objects absorb the red and reflect the
higher (short-wave) frequencies, one thinks of green as a "cool" colour.
So, your red t-shirt will absorb the high
frequency part of the light and your green one will absorb low frequency
part of the light. Because E=hU, your red t-shirt
will absorb more energy than your green one, and this energy will be happen
as heat. That is why people wear light coloured
clothes during summer and dark coloured during winter.

I hope I have been helpful in answering your question.
Keep being interested in science and remain curious! ;)

Yan Garnier, applied chemistry, Napier University, Edinburgh-UK.
ranx003@hotmail.com

Sources: The physics and chemistry of color, by Kurt Nassau.
The colour eyes, by Robert Cumming & Tom Porter.