# Is colour dependent on wavelength of frequency?

## Main Question or Discussion Point

EDIT: title should be Is colour dependent on wavelength or frequency

Okay, and so here is the question in my mind.

We all know (or at least taught) that when light enters an optically denser medium, it slows down and its wavelength shortens. Frequency, however, remains the same.

Going by the above, will we see (or at least theoretically conclude) that there is a change in colour observable?

If colour is determined by wavelength, then the above should see a blue-shift.

If colour is determined by frequency, then the above should see no change.

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It would seem to me that color is a perception and therefore dependent on how your eyes receive it. That, to me, would make it frequency based. To me, a change in wavelength without a change in frequency would imply a change in the speed of light. I doubt your eye cares at what speed light hits it but as long as your internal timing were not thrown off my it, would interpret the frequency as normal and would perceive the wavelength as the normal wavelength for that frequency.

The actual speed of light is the same in any material. It's just that a photon bumps into an atom once in a while. After absorbing the energy from the photon, an electron in the atom gets into a higher energy excited state. It doesn't take long for the electron to go back to it's ground state and emit a photon (light) while doing that. So it seems like the speed of light has changed, but what's actually happening is that it bumps into atoms that 'absorb' the photon for a little while.

Oh, and I forgot to mention that the frequency of the emitted photon depends on what kind of atom it is. So it might change color, but not necessarily. Correct me if I'm wrong.

in my point of view color depends on wavelength so if shift in wavelengt cause the shift or change in color

Andy Resnick
Because frequency is a measure of energy while wavelength a measure of momentum, it's probably more relevant to think of 'color' in terms of frequency (since not only visual perception, but cameras and calorimetric detectors are based on absorption).

Think about it....if color was dependant on wavelength.....would'nt the color change in different mediums?

i.e wavelength of yellow is 600nm and of blue is 400nm. Does that mean a yellow object appears blue in water(ref.ind=1.5 approx)??????

Thats absurd.
Of course color depends on frequency.....because frequency remains unchanged in different media of propogation.

The rods and cones in the eye are stimulated to vibrate to different frequencies depending on the frequency of incident light.
This causes color perception

BOTTOMLINE - Color is percieved by frequency.

WHHHHHHAT IS THHHHHHHHHIS?
1.Do check ,pleas sir, meters you are trying to say befor submiting them; pleas.
There is no such deference betueen what wave lenght and frequency Sir!.
the two are related by two contats c and h ( light speed and Plank constat).
If one changes the othor does imediatly.
It is so ""rediculus"" to say that one changes while the othor ""remains" the same.
2.When photons across a material the light speed becomes less , yes, but that affects every thing...p, E, wave lenght, frequency...every thing changes respectfuly to n the refraction index.
3.I do believe you are talking, or trying to talk , about the diferrence of energy: where is it?, ahd here yes , this is the good question and it have been put since decades, but recently there is some progress.
(Thanks, and sorry for any thing)

MATLABdude
EDIT: title should be Is colour dependent on wavelength or frequency

Okay, and so here is the question in my mind.

We all know (or at least taught) that when light enters an optically denser medium, it slows down and its wavelength shortens. Frequency, however, remains the same.

Going by the above, will we see (or at least theoretically conclude) that there is a change in colour observable?

If colour is determined by wavelength, then the above should see a blue-shift.

If colour is determined by frequency, then the above should see no change.

The above responses give you the theoretical explanations of what happens when light enters one medium from vacuum or air. The (macroscopic) speed of light decreases (because the medium it enters has higher index of refraction), and the propagation wavelength increases, while frequency stays the same (as you say).

However, note that this light would then enter your eyeball, and change speed / wavelength again. But that's okay, because, as in all other cases, frequency remains constant. The speed / wavelength in your eye is the same as if you were seeing this light in air. Same thing happens when you have a camera (assuming the inside of your camera is air tight!)

While the above is an aide to understanding, it's a little misleading. As others have said above, the energy of any photon in this light beam is what causes the cones in the back of your eye to respond, or the elements of a CCD (charge capture device; i.e. the image taking part of your digital camera) to respond, regardless of what's in front of it.

WHHHHHHAT IS THHHHHHHHHIS?
1.Do check ,pleas sir, meters you are trying to say befor submiting them; pleas.
There is no such deference betueen what wave lenght and frequency Sir!.
the two are related by two contats c and h ( light speed and Plank constat).
If one changes the othor does imediatly.
It is so ""rediculus"" to say that one changes while the othor ""remains" the same.
2.When photons across a material the light speed becomes less , yes, but that affects every thing...p, E, wave lenght, frequency...every thing changes respectfuly to n the refraction index.
3.I do believe you are talking, or trying to talk , about the diferrence of energy: where is it?, ahd here yes , this is the good question and it have been put since decades, but recently there is some progress.
(Thanks, and sorry for any thing)
2) Uh huh, what are you trying to prove with this claim? Besides, did you say frequency changes with refraction index? Does that imply energy lost or energy gain?
3) And no, i'm not talking about energy.

so from responses i gathered, the colour perceived is dependent on frequency and not wavelength. Am I right?

So if i shine a beam of monochromatic light from air into water, and observe the beam in the water, the colour observer should (theoretically) be the same?

Doc Al
Mentor
WHHHHHHAT IS THHHHHHHHHIS?
1.Do check ,pleas sir, meters you are trying to say befor submiting them; pleas.
There is no such deference betueen what wave lenght and frequency Sir!.
the two are related by two contats c and h ( light speed and Plank constat).
If one changes the othor does imediatly.
It is so ""rediculus"" to say that one changes while the othor ""remains" the same.

2.When photons across a material the light speed becomes less , yes, but that affects every thing...p, E, wave lenght, frequency...every thing changes respectfuly to n the refraction index.
3.I do believe you are talking, or trying to talk , about the diferrence of energy: where is it?, ahd here yes , this is the good question and it have been put since decades, but recently there is some progress.
(Thanks, and sorry for any thing)
This is almost completely incorrect.

so from responses i gathered, the colour perceived is dependent on frequency and not wavelength. Am I right?

So if i shine a beam of monochromatic light from air into water, and observe the beam in the water, the colour observer should (theoretically) be the same?
Yes; you have understood the postings the same as I have understand them. So, surely you are correct.

Doc Al
Mentor
so from responses i gathered, the colour perceived is dependent on frequency and not wavelength. Am I right?
Yes. (Though as MATLABdude stated, once the light enters your eye the wavelength depends on the index of refraction of your eye, not on any other medium it might have passed through.)

So if i shine a beam of monochromatic light from air into water, and observe the beam in the water, the colour observer should (theoretically) be the same?
Yes.

So cool.....we reached a conclusion...........

rcgldr
Homework Helper
Color is dependent on the frequency or frequencies and the senstitivity of the 3, or in some cases, 4 types of color receptors in humans to frequencies. A single frequency or combined frequencies can appear to be the same color if the receptors are stimulated by the same amount and ratio. Some perceived colors are only possible as a combination of frequencies as opposed to a single frequency (non-spectral colors).

I do appologyte for my weak language.
But, I do wonder if here -in this place- gathor people who studied real physics or are studying, or it is no more than high school pupils, talking physics like science fiction.

Whan two mesures-in physics- are related by a number, we do say Sir, they are one measure, because once we know one we deduce the othor immediatly. That is why we say wavelenght and frequency are one mesure, means, in experiment field, no difference!.
every body can discuss this , but in the stage of mesure,just take it like this.
Question;
what are the equation you use to proof that frequancy remains the same, in this case we are talking about?.
I can be more direct althought of every thing and anwser (or at least try to ), Mr who did put the question in the first place-this Mr who does not know that some scientist did enter in a long debate about the lost or gain of energy- ,
Sir, let say that color dependes on frequancy,
But frequency depends on wavelenght ,
then wich one of them?,
I do not find the question strange, but stranger, the answers given.
Thankyou,

I do appologyte for my weak language.
But, I do wonder if here -in this place- gathor people who studied real physics or are studying, or it is no more than high school pupils, talking physics like science fiction.

Whan two mesures-in physics- are related by a number, we do say Sir, they are one measure, because once we know one we deduce the othor immediatly. That is why we say wavelenght and frequency are one mesure, means, in experiment field, no difference!.
every body can discuss this , but in the stage of mesure,just take it like this.
Question;
what are the equation you use to proof that frequancy remains the same, in this case we are talking about?.
I can be more direct althought of every thing and anwser (or at least try to ), Mr who did put the question in the first place-this Mr who does not know that some scientist did enter in a long debate about the lost or gain of energy- ,
Sir, let say that color dependes on frequancy,
But frequency depends on wavelenght ,
then wich one of them?,
I do not find the question strange, but stranger, the answers given.
Thankyou,
I agree. Wavelength = speed of light / frequency. Speed of light is a constant. So if you know one, you know the other. So you could say that color perception depends on frequency, but it would mean the same as saying that it depends on the wavelength.

And the fact that your eye has a refractive index doesn't change the frequency/wavelength (??)!

Doc Al
Mentor
I do appologyte for my weak language.
But, I do wonder if here -in this place- gathor people who studied real physics or are studying, or it is no more than high school pupils, talking physics like science fiction.
Sounds rather melodramatic.

Whan two mesures-in physics- are related by a number, we do say Sir, they are one measure, because once we know one we deduce the othor immediatly. That is why we say wavelenght and frequency are one mesure, means, in experiment field, no difference!.
every body can discuss this , but in the stage of mesure,just take it like this.
Question;
what are the equation you use to proof that frequancy remains the same, in this case we are talking about?.
I can be more direct althought of every thing and anwser (or at least try to ), Mr who did put the question in the first place-this Mr who does not know that some scientist did enter in a long debate about the lost or gain of energy- ,
Sir, let say that color dependes on frequancy,
But frequency depends on wavelenght ,
then wich one of them?,
I do not find the question strange, but stranger, the answers given.
Thankyou,
I agree. Wavelength = speed of light / frequency. Speed of light is a constant. So if you know one, you know the other. So you could say that color perception depends on frequency, but it would mean the same as saying that it depends on the wavelength.
Perhaps I'm misinterpreting what you both mean, but the speed of light does change when light travels through a dielectric medium. The wavelength--but not the frequency--changes.

Note that this is a bulk phenomena of light interacting with the medium. Even though photons themselves only exist at speed c, their effective speed is reduced as they travel through the medium.

what are the equation you use to proof that frequancy remains the same, in this case we are talking about?.
Well, not exactly an equation, but in physics, the frequency of a wave is a property of the source emitting the wave, while the wavelength of the wave is a property of the medium through which the wave travels. So, I would say that people are correct in saying the perceived colour of the source depends on the frequency...

EDIT: title should be Is colour dependent on wavelength or frequency

Okay, and so here is the question in my mind.

We all know (or at least taught) that when light enters an optically denser medium, it slows down and its wavelength shortens. Frequency, however, remains the same.

Going by the above, will we see (or at least theoretically conclude) that there is a change in colour observable?

If colour is determined by wavelength, then the above should see a blue-shift.

If colour is determined by frequency, then the above should see no change.

In vacuo, color is determined reciprocally by either frequency or wavelength, where their product equals the speed of light.

The cosmological redshift or blueshift thus effects both.

As has been alluded to in previous posts, light traversing an optically dense medium undergoes a change in wavelength, represented by either a positive or negative refractive index.

Speculation:

In an optically dense medium, interference with light seems to concern space-based interactions rather than time-based.

How linear is a diffracted light beam's path, considering it has at least two boundary conditions (theoretically remote in time) to satisfy?

A photon created at the center of the Sun takes around a million years to reach the surface. No kidding!