# How do we know that human eye reacts on frequency of visible light rather than on some other parameter? [duplicate]

This is a very basic question in optics: why the mathematical language we use corresponds to what we actually see.

There are (at least) two ways to think of a decomposition of a visible light.

One way is experimental: when a beam of light passes through a glass prism it decomposes to many beams according to their color. These colors are perceived by human eyes.

The second way is theoretical: the light is thought of as electromagnetic wave satisfying the Maxwell equaitons in vacuum. Then one uses the Fourier transform with respect to the time variable to decompose a given solution as a combintaion of solutions of the form $$\vec E(\vec x)e^{i\omega t}$$.

If I understand correctly it is claimed in all stadard textbooks in optics that the above two decompositions correspond to each other in the sense that the frequancy $$\omega$$ determines the color of the light. Why? How do we know that the color is determined by the frequency of light and not by some other parameter? I could not find any clear explanation of this correspondence so far. A reference would be helpful.

Remark. There is a similarly sounding question What determines color -- wavelength or frequency? It is different from my question, and the answers there do not answer my question.

• @MKO Different photoreceptive chemicals in retina need different energy to get into an excited state and initialize a proces of sending a signal to the brain. So the retina actualy reacts to the energy of the photons, but it is directly correlated to the wavelength (longer wavelength = lower energy, $E = \frac{\hbar c}{\lambda}$) – Adam Latosiński Sep 29 '20 at 8:49