An Etymological Dictionary of Astronomy and Astrophysics

A unit of radiation energy sometimes used in the investigation of
photochemical processes. The unit is defined as
N_Ahν, where N_A is → Avogadro’s number and hν is the energy of a → quantum of the radiation. One einstein (or Einstein unit) is the energy per → mole of photons carried by a beam of monochromatic light.

See also: Named for Albert Einstein (1879-1955).