In Which Way Is a Photon of Blue Light Similar to a Photon of Red Light?

Light from blue and red photons has energy but no mass, has no electrical charge and travels at the speed of light. All photons share these properties, no matter their energy level. A photon’s color comes from its wavelength, with blue having a higher value than red.

Colors visible to the human eye represent a small portion of the entire electromagnetic spectrum. All photons, visible or not, carry energy expressed through wavelength. The wavelength determines how the photon interacts with other elementary particles. Photons in the gamma or X-ray end of the spectrum can penetrate most matter because they possess very high wavelengths. Photons in the visible spectrum, having much lower wavelengths, tend to either reflect off matter or be absorbed by it. This property explains why humans see color as they do.

It wasn't until the 1960s that physicists could study specific colors and wavelengths of photons using lasers. Subsequent study revealed no differences in photon properties beyond wavelength, although numerous applications using coherent light produced by lasers have become commonplace.

While photons appear to have no mass, they do interact with other fundamental particles. Max Planck and Albert Einstein laid the groundwork for quantum physics while studying light and radiation. Planck proposed that energy radiated in discrete packets he named quanta and showed how energy would be carried by quanta. Einstein showed how these quanta could produce electric current when light shines on specific materials, suggesting that the photons, while having no mass, could dislodge an electron in an atom. This was the photoelectric effect, and it won him a Noble prize.