•Albert Einstein's mathematical description in 1905 of how it was caused by absorption of what were later called photons, or quanta of light, in the interaction of light with the electrons in the substance, was contained in the paper named "On a Heuristic Viewpoint  Concerning the Production and Transformation of Light". This paper proposed the simple description of "light quanta" (later called "photons") and showed how they could be used to explain such phenomena as the photoelectric effect.