Excerpted from Produce Grower

Patrick Williams, author


Both Hernandez (assistant professor in North Carolina State University’s Department of Horticultural Sciences) and PARsource division manager Ron James make the point that lighting for horticulture is more nuanced than lighting for human use. For instance, James says, the light spacing for growing plants needs to be closer together than the light spacing for architectural applications. 

PARsource bases its lighting designs on numerous factors. “When we do our designs and we’re moving around and we’re calculating the overlap, there’s times that this reflector’s better, there’s times that this reflector’s better and there’s times that this reflector’s better,” James says. Reflector designs are based on light spectrum, but also on factors such as light distribution and uniformity. 

James recommends growers work with a lighting manufacturer that sells all technologies so that they can find the right fit. Growing conditions vary for growers in different locations, operating under different conditions and growing different crops. For example, greenhouse produce growers in Michigan versus Texas, or growing tomatoes versus lettuce, need different amounts of light. 

With LEDs, James says, growers can control the spectrum and don’t have to worry about there being as much heat as with other light types. Other newer lighting technologies include double-ended high-intensity discharge (HID) lights and ceramic metal halide HIDs, James says. Double-ended lamps have a high PAR output and more blue light than high-pressure sodium (HPS) lamps. Ceramic metal halides also give off a large amount of blue spectrum light, and they have a double-glass jacket. “Metal halide is more for vegetative growth versus fruiting flowering, and that’s why people kind of like it,” James says.