SI physiological units

One of the seven base units of the International System of Units (SI), the candela, which is the unit of the luminous intensity, and its derived units are physiological units. The effect of the optical radiation on human beings is taken into account by introducing a weighting factor, the luminous efficiency, to the definition of radiant quantity of interest. Some SI physiological units are frequently used in other metrological domains, such as ionizing radiation, photochemical and biological activities, acoustics and photobiology. This communication is intended to present some principles underlying the definitions of physiological quantities and units associated to these metrological fields.