powered by a power supply 60 preferably the pcb 52 is connected to the power supply 60 by wires 62 and the power supply 60 is remote from the light engine for example the power supply 60 could be placed under the plants 24 to prevent it from blocking any of the natural sunlight the power supply can power more than one light engine an attachment hook 44 or other mechanical attachment means is used to attach the rail 34 to the greenhouse frame 22 the attachment hook 44 is attached to the rail 30 at the mounting slots 42 the attachment hook 44 is attached to the roof of the greenhouse or to an existing support frame 22 the light engines are relatively light thus the greenhouse can be built so the frame can support the greenhouse extra weight of the lamps does not need to be a consideration when determining the frame strength and or design further the leds can be located close to or away from the plants thus the light engines can be retrofit on an existing greenhouse frame in addition because the leds do not have to be kept away from the plants the greenhouse can be built lower to the ground this saves materials and may allow lighter weight frames to be used it may also allow for reduced heating and or cooling costs since the area to be heated or cooled may be smaller than in conventional greenhouses in one embodiment the rails and light engines are approximately the same length and a plurality of rails 30 each with a light engine are used for each row where.