Radiation Measurement in Photobiology — Choice of Units

The physical units most commonly used in photometry have limited value outside the field of illumination engineering. They tend also to conceal rather than display the physical concept of radiation as understood at present.Only by making the concepts of quantum theory accessible by a fundamental change of units, can those concepts make their full contribution to photobiology. The paper suggests adoption of the quantum as the unit of intensity and the electron volt as the specification of spectral quality, thus bringing the nomenclature of photometry into line with other branches of radiation physics. A start is made with definition of some of the essential derived units, source intensity, irradiation, and flux.