# Color of Light

1. Oct 21, 2008

### Gear300

What property of visible light defines its color, the wavelength or frequency (or something else)?

2. Oct 21, 2008

### HallsofIvy

Staff Emeritus
A very strange question. That looks to me like something you are expected to look up. Are you aware that aware that frequency*wavelength= (number of waves per second)*(length of one wave)= distance light travels in one second= speed of light?

3. Oct 21, 2008

### Gear300

Yes, I am aware of that. I was reading a bit on dispersion; the index of refraction for a medium is inversely related to the wavelength of incoming light so that if a beam of white light was incident on a prism, it would lead to a dispersion of the different colors. What got to me was that since the wavelength and speed of light change when entering a different medium, wouldn't that imply that if a ray of green light were to be incident to a surface, wouldn't it change color while in the new medium (although, the frequency is the same)?

4. Oct 21, 2008

Staff Emeritus
Ah...this is actually a physiology question. The question is whether the cones in our eyes respond to frequency or wavelength.

I'll answer your question with a question: if you are swimming (and your eyes are under water), does a red object still look red?

5. Oct 21, 2008

### borgwal

It's the frequency that doesn't change when going from one medium to the other, but the wavelength does change. It's also the frequency that determines the energy of a photon and that determines whether an atom or molecule (in your eye, for instance), absorbs the photon or not. So, in that sense, frequency determines color.

6. Oct 22, 2008

### Gear300

The way I'm thinking of it is whether somebody is underwater or not, the light still enters the eyes. In that case, the final medium would ultimately be the parts of the eye. So, if light has a frequency/wavelength for green while in vacuum, then regardless of whether its in some other medium, its considered to be green light (since that is what the eyes will associate as green).

I see...this makes good sense...
There is one more question I have...
Color is more or less a subjective phenomenon, right?