The wavelength sensitivity for decrease in percent elongation at break of ethylene carbon monoxide copolymer (EGO) and a low density polyethylene containing a metal compound prooxidant (LDPE/MX) on exposure to a borosilicate-filtered xenon-are source was determined using a set of sharp cut-on filters. The spectral region primarily responsible for the degradation at 60 degrees C is 323-328 nm for ECO and 323-338 nm for LDPE/MX. At 77 degrees C, the sensitivity shifts about 10 nm to longer wavelengths. Based on the wavelength sensitivity of these materials to solar simulated radiation and the transmission properties of window glass, these materials can be expected to lose desirable mechanical properties when exposed to window-glass-filtered sunlight.