PHYSIOLOGICAL UNITS IN THE SI

A modified system of SI units is described that includes a new categor y of ''physiological units''. In this system, physiological units are a special class of derived units that are defined with respect to spec ified reference stimuli for the purpose of calibrating the nominal hum an response to external physical effects. This new category includes t he unit of luminous intensity, the candela, and the unit of dose equiv alent, the sievert. By comparison with the current SI, in the modified SI the candela is classified as a physiological derived unit instead of as a base unit and the definition of the sievert is revised to incl ude specification of the reference radiation.