Light traps are an essential feature of any light deprivation greenhouse operation. They are placed over any ventilation opening in the greenhouse structure in order to block light without sacrificing the efficiency of the fans they cover. Light traps should match the size of the fan with which they are used. Larger greenhouses call for greater ventilation and subsequently bigger light traps. When using them correctly, growers no longer have to choose between proper ventilation and total darkness inside their greenhouses.