# Any Color You Light

1. Apr 3, 2012

### Newtons Apple

( Pink floyd joke in the title..from Dark side of the moon...which incidently has the light prism on the cover...) Hey everyone... Question from a most curious student... The color we see, the red on my flash drive, the green of the money in my wallet, or the blue of my shirt, what am I actually seeing? I know that the entire wavelength of light, all the colors mixed together, hit the object in question, and what's reflected is the color we see...But what causes the reflection or absorbtion of certain colors. If I have green paint of something, why does it absorb all the other colors except green? Or likewise, if I have a brown desk, what in the desk's make up, is causing the other waves of colors to be absorbed except the brown? (which is blue green I think?)

Last edited: Apr 3, 2012
2. Apr 4, 2012

### GrimReapiN

Good question, I was curious so I google'd around and learned something new!

The selective absorption of light by a particular material occurs because the selected frequency of the light wave matches the frequency at which electrons in the atoms of that material vibrate. When the two frequencies match, the electron absorbs the energy, never to be seen. -http://www.physicsclassroom.com/class/light/u12l2c.cfm

In short- Electrons absorb some of the light frequencies, the frequencies left are the ones you see.

Also, when the energy is absorbed, the electrons create thermal energy. That may be why during the summer a black car is hot to the touch, but a white car isn't (as hot). But that's just my speculation, would be totally awsome if that's why! :tongue:

Hope I've helped. :shy:

Last edited: Apr 4, 2012
3. Apr 4, 2012

### Staff: Mentor

That is right.

>> When the two frequencies match, the electron absorbs the energy, never to be seen.
At least there is a chance to have this. Another option is that the electron just releases the energy again and emits a photon - which might reach your eye. But the basic idea is that you have to look at the structure of the material: Which wavelengths can it absorb, what happens afterwards?

4. Apr 4, 2012

### Khashishi

Your eyes have three (or four if you are lucky) different kinds of color receptors ("cones"). Each type of color receptor has a photon response curve peaked at a different value of wavelength. So, some colored light will hit your eyes and stimulate your cones in some ratio. You perceive the ratio of cone stimulations as a color.

With three photoreceptors, the space of colors and intensities that we can perceive is 3 dimensional, but the space of possible light combinations is infinite dimensional (# of functions of intensity vs frequency). What this means is that many different light combinations appear the same color to us.

Just because something is green doesn't mean it is only giving off "green" photons.

Last edited: Apr 4, 2012