Five different combinations of fluorescent tubes (UV-B/UV-B, UV-B/UV-A, UV-A/UV-A, UV-B/White, White/White) were used to determine relative effects of UV and visible light on the nucleopolyhedroviruses (NPV) of Helicoverpa zea and Spodoptera exigua. For both viruses, the greatest inactivation occurred with exposure to UV-B radiation. Both virus concentration and radiation exposure time influenced the rate and degree of inactivation. In the case of the UV-A/UV-A and White/White combinations inactivation occurred only with the longest exposure (24 h) and the lowest virus concentration (0.747 PIB/mm²). The NPV from H. zea was found to be more sensitive to UV radiation than the NPV from S. exigua.