A white light, as we all know, is composed of seven lights VIBGYOR. Each of the component lights has distinct frequency ranging from one value to another. So, when the photons have wavelength of 600 nm it becomes a yellow light and when it changes to 700 nm it becomes a red light. So, does this imply that the frequency with which a group of photons vibrate determine the colour of light? Well, in that case, with what frequencies are photons vibrating for a white light?
To get a perception of a white light, one has to observe simultaneously many photons having different frequencies and obeying a certain distribution function.
Keep in mind that a color is not a physical property, since it is resulted from human brain's interpretations of signals coming from eyes receptors.
Light that our eyes, or other system of detectors, would perceive as "white" could have several different maekups:
It could be a stream of photons all in different energy / momentum eigenstates. That is, there could be a population of photons, some of which are red wavelength, some blue, some green and so forth as in freude's answer; OR
It could be made up of photons all in exactly the same quantum state. You really can have one, lone, sole "white" photon all on its own. A photon, like any other quantum object, can be in a pure quantum superposition of basis eigenstates (eigenstates of whatever observable you care to work with). There is no reason why a photon has to be in a pure energy / momentum eigenstate. Its state could be such that there is a complex amplitude $\psi(\nu)$ to be observed at wavelength $\nu$. For more information about this idea, see my answer to the following question How can we interpret polarization and frequency when we are dealing with one single photon?
The answer to what electromagnetic frequency "white" is rather both a simple and a complex answer all wrapped into one explanation; here goes...
We all know that the color "white", if you want to call it that, is a combination of all of the visible light frequencies. Therefore logic dictates that the frequency of "white" must then be "all" frequencies.
Despite this though, this then brings up the age old allegory of which came first the chicken or the egg. That is, it begs the question of which came first, the color “white”, or it components of the red, green, and blue visible spectrums? It would seem to me that the answer to this would be that “white” came first as a byproduct/reaction of photonic assimilation into the void we call darkness. (Provided of course that said photon had matter/mass to interact with.) My thoughts are that “white” came first.
However this is not the end of the frequency question, as once the color “white” is obtained there is actually no true blue, red, and green individual frequencies, as the individual spikes of those frequencies would then all have to be simultaneously peaking at the same instant in time; lest the “white” light would be an impure off-white. That is, at that instant where pure “white light” is visible there is actually no waveform pattern, as all of individual peaks of blue, red, and green are in linear synchronicity.
Those are my scientific thoughts.
As for my philosophical standpoint I am pondering all that we have heard throughout ours life’s about us being creatures of light; that the Almighty is the Alpha and the Omega, the Beginning and the End; that I Am is in and around everything all of the time; and that we are all created in His image?
Could this be why the persons in the bible, and since that time, have all described the presence of GOD as emanating pure white light that was so intense that they would have to shield their eyes from it? Could it be that in our current dimension of matter/mass, GOD would appear, consistent with principles of physics, as a combination of all of the electromagnetic frequencies both visible and invisible, all at one time, and in the same astral plane?
I believe that there is something to this that requires further meditation and prayer.
God Bless All.
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