The First and Second Principle of Photochemistry

Akimoto, Atmospheric Reaction Chemistry, Springer Atmospheric Sciences, DOI 10.1007/978-4-431-55870-5 2 

The second principle of photochemistry is called the photochemical equivalence law, or the Stark-Einstein law, which states the absorption of light occurs in the quantum unit of photon or one molecule absorbs one photon, and one or less molecule can be photolyzed accordingly.  

Instead of molecule, moles (1 mol = 6.022 x 10 molecules Avogadro number) are often used in experimental chemistry. The unit of photon energy referenced to one mole is called an einstein. Photon energy per 1 einstein of light with wavelength X (nm) is expressed as 

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