A photon, belongs to the class of bosons, is the smallest discrete amount or quantum of electromagnetic radiation. It might be the most familiar of elementary particles. As photons are massless, they are traveling at the constant speed of light $$(= 2.998 \times 10^8$$ m/s$$)$$ and bombard us daily from the sun, moon, and stars. For more than a century, scientists and engineers have harnessed them in aggregate to illuminate our cities and now, our screens.