Abstract: A travelling lighting system for a greenhouse includes a plurality of lamps supported on an elongated truss which is slowly advanced back and forth across a greenhouse bay to provide lighting for the plants therein. The truss may be supported by trolleys carried in a pair of parallel spaced apart tracks extending the length of the greenhouse bay. A power drive system advances the truss along the tracks. A power cord support rail may be provided above the truss to collect and support the electrical power cord to the truss at spaced apart locations along the cord to prevent sagging as the truss is advanced toward the electrical power source.