Fourteen representative visible light-cured composite materials, including a total of 29 shades, have been examined for sensitivity to ambient light. The assessment was based upon a procedure recommended in an International Standard (ISO/DIS 4049). All but four of the 29 formulations exceeded the critical working time of 60 s when exposed to ambient illumination of 20 klx. These four composite resins exhibited working times greater than 60 s under 10 klx illumination, and the maximum working time observed at 10 klx was 227 s. These data confirm the finite working time of light-cured resins under clinical lighting conditions.