AbstractThe degradation of plastics by ultraviolet energy and the use of protective ultraviolet absorbers to improve stability necessitate studies along several lines. These include (a) the measurement of the ultraviolet spectral energy distribution of sunlight and of the indoor accelerated test sources, (b) the measurement of the extent of degradation as a function of the wavelength of the incident radiation, (c) an estimate of the absorbing effectiveness of the added protective agents, and (d) the stability of the protective ultraviolet absorbers themselves.