Supplemental Lighting

Figure 17: HID supplemental greenhouse lighting. Source: Scott Sanford

Figure 17: HID supplemental greenhouse lighting. Source: Scott Sanford

Growers might use supplemental lighting for several reasons. It can shorten or help control time-to-market, produce higher quality plants or induce earlier flowering. T-8 or T-5 fluorescent lamps are recommended for growing chambers while high intensity discharge (HID) lamps are recommended for greenhouses (Figure 17). There are two types of HID lamps used in greenhouses: high-pressure sodium and pulse start metal halide. High-pressure sodium lamps are the most efficient and emit a yellow/orange light. A pulse-start metal halide lamp emits a bluish/white light. Typically, either high-pressure sodium lamps or a 50:50 mix of both types are used in greenhouses. Lights should be controlled with timers, or better yet, a light integral controller that measures the sunlight entering the greenhouse daily and controls the lights to provide supplemental light to reach a minimum daily level.