Do individual photons of light each contain all the colors of the light spectrum or is each single photon a single color?

Question

Do individual photons of light each contain all the colors of the light spectrum or is each single photon a single color?

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Answer 1

Each photon is a single “color”. More specifically, each photon has a particular wavelength (or frequency) which corresponds to what we perceive as color. I think it’s important to note that human vision is somewhat subjective and more complicated than merely absorbing a photon and detecting its wavelength.

Without going too deep into it, our eyes only have three kinds of detectors and a particular wavelength of light will stimulate *some* of them some of the time, and it’s the combination of which detectors that are stimulated that our brain interprets as *color*. Our brains also do a lot of things like correcting for shadows and lighting and whatnot. Our vision can be tricked by absorbing several photons with different wavelengths. For example, each pixel in your screen is made of three sub-pixels, which are red, green, and blue. The screen never emits “yellow” photons: instead, it lights up the red a little bit and the green a little bit, which stimulates our eyes just like a yellow light.

Regardless: photons are emitted when charged particles (like electrons and protons) lose energy. The wavelength of the light corresponds with how much energy the particle lost. Typically this comes from an electron being energized into a higher “orbit” around its nucleus and then dropping back down into a lower “orbit,” emitting a photon in the process. Charged particles will absorb a photon and gain energy – which for an electron means going up to a “higher” energy state.

More energy in the photon means it has a smaller wavelength (and higher frequency). The electromagnetic spectrum – all of the energy levels that photons can have – goes from very very big radio waves (technically they can be as large as the universe but typically you’re looking at kilometers to meters) to microwaves to infrared light to all the visible light (which is a tiny little slice of the whole spectrum) to UV, X-ray, and gamma.