LOW AND MODERATE IRRADIANCES OF UVB AND UVC IRRADIATION ARE EQUALLY ERYTHEMOGENIC IN HUMAN SKIN

—The effect of irradiance on ultraviolet-induced delayed erythema was studied in normal human skin. With both UVB and UVC radiation, the minimal erythema dose was the same whether exposure lasted several seconds or 5 h. A reciprocal relationship between exposure duration and irradiance has previously been shown to exist for exposures ranging from nanoseconds to minutes. The present study shows that even if exposures last over 4 h the minimal erythema dose is a function of exposure dose and not of irradiance or exposure duration.