# Wavelength of light (air vs. water)

1. May 25, 2005

### bullroar_86

from my notes:

red light has a wavelength of ~660 nm

I just did a question where I was asked to find the wavelength in water..

I got an answer of 470 nm.

Just curious why the color doesnt change. (a red bathing suit is still red under water)

I'm thinking the "red = wavelength of 660 nm" only applies to air, and that figure varies with different mediums.

Is this the explaination?

Last edited: May 25, 2005
2. May 25, 2005

### dextercioby

Okay,try to look at this chick's red bikinis with your eyes underwater.Is it the same color ...?

Daniel.

3. May 25, 2005

### bullroar_86

Unfortunately, I'm currently lacking in the "chick in a red bikini" dept.

but my guess would be yes it is the same color..

I'm just not sure on the explaination

4. May 25, 2005

### dextercioby

Daniel.

5. May 25, 2005

### bullroar_86

Well the only thing I can come up with is what I already posted

I'm thinking the "red = wavelength of 660 nm" only applies to air, and that figure varies with different mediums.

So in different mediums the wavelength for red is different, so maybe in water its 470 nm, and it could be something different in glass etc..

6. May 25, 2005

### HallsofIvy

Staff Emeritus
The crucial point for color is frequency, not wavelength. So, yes, "red" light- that is light of that frequency has slightly different wavelengths in different media.

7. May 25, 2005

### dextercioby

It wouldn't matter any way,because light passes through a lot of optical media before hitting your yellow spot at the back of retina...And it is the frequency of the light (energy) that affects those analyzers.

Daniel.

8. Apr 6, 2010

### crimsonclear

Old post, but this should be clarified.

If you are looking at a person in a pool wearing red shorts, why are their shorts still red even though the wavelength of the light has been modified by water's refractive index.

As the above poster pointed out, the frequency of the light does not change (as the original source is still at the same hertz, wiggling the electrons on the surface at its frequency), but the wavelength of that specific color inside a substance does.

This can be easily explained if i can make this diagram make sense:

----light @ ~660nm----> [water, wv @ 470nm]>----as light exits water, the wv will return very quickly to 660nm-----> [your eye]

So, the 'color' of the light actually does change, but as the light is scattered back out of water, it returns to its original wavelength.

I had originally wondered why when you are inside water you don't see the color change, but once the light leaves the water and enters your eye, it is no longer being subjected to the refractive index of water, and it will speed up to the normal refractive index of your eye (which is normal color to us)