Re: How does light become heat?

Objects absorb electromagnetic waves (our eyes detect them, too) 
of a range 
of energies.  The electromagnetic spectrum encompasses waves of 
all 
different kinds of energies.  On the low-energy side are radio 
waves; the 
high-energy side contains X-rays and Gamma rays.  In the middle 
somewhere 
is the visible region:  this is the part we can detect with our 
eyes.  The 
two regions around the visible region are infrared (IR) at lower 
energy, 
and ultraviolet (UV) at higher energy.  Here's depiction of this:

radio	infrared	visible	ultraviolet	X-rays	Gamma rays
low energy	------------------->	high energy

By the way, there are other categories of the spectrum which are 
not 
included above (like microwaves that we use to cook).  This is OK, 
since 
the most important regions for this question are IR and visible.

Objects absorb a significant amount of IR radiation, as well as 
visible.  
This absorption causes the atoms in the object to become excited.  
When 
they get excited, they have more energy than they had before, so 
they move 
more.  When they move more, they collide, and this causes heat to 
be 
emitted.  So, all that's really going on is a transfer of energy:

Light energy ->	electronic energy (atoms excited)	-> heat

So, why do black objects get hotter than white ones?  This has to 
do with 
the absorption of the visible part of the spectrum.  Black objects 
absorb 
the entire visible spectrum, and reflect none of it; this is why 
they 
appear black to our eyes.  White objects absorb none of the 
visible, and 
reflect it all back; this is why they appear white to us.  Colored 
objects 
absorb part of the spectrum and reflect back the energy that is 
left.  
Since black objects absorb all that energy, they give off more in 
the form 
of heat.