Dosage Units for Biologically Effective UV-B: A Recommendation

Abstract

In the earlier panel discussion on action spectra, a case has been made for the pivotal role played by action spectra when used as weighting factors in the calculation of biologically effective UV-B radiation. This is of import not only for the determination of radiation amplification factors but also for relating the dosage received from lamp systems to that received from the sun. Because both biological photochemical reactions and the spectral irradiance from the sun change so rapidly as a function of wavelength, all would agree that total irradiance, or fluence rate, is of little value in determining UV-B dosage. Instead, it is preferable to speak of “weighted” or “effective” irradiance, either at a single wavelength, or integrated over a particular waveband. A familiar analogue is the use of a “standard eye” action spectrum as a weighting function to calculate luminous energy. When integrated with respect to wavelength, this constitutes illuminance, normally expressed in units of lux. Although special units have been contrived in the case of illuminance, confusion in the literature could be greatly minimized for other types of biologically effective radiation if one speaks of “weighted” or “effective” irradiance, and employs SI units. Thus, the integrated weighted irradiance can be expressed as effective Wm⁻² or photons m⁻² s^−l. Different unitless weighting functions can be substituted as the occasion warrants as long as these are clearly specified.