Indoor Growing & High Pressure Sodium Lights


Plants kept indoors require special lighting to enable them to grow, flower and fruit. One of the best ways to simulate natural sunlight is to grow indoor plants under high pressure sodium lights, also called HPS lights. Commercial growers favor HPS lights to raise plants indoors because they are the most efficient indoor grow lights. In addition, they are less expensive to run than incandescent bulbs. They consume the same amount of energy as an incandescent bulb but last much longer. In addition, HPS lights are six times brighter.

High Pressure Sodium Lights

HPS lights are generally used for indoor growing when it is time for the plants to start budding, flowering and fruiting. The reason for this is that HPS lights emit light from the orange and red part of the electromagnetic spectrum. This is the type of light required for plants to flower and fruit. During the vegetative growth, plants require light from the blue area of the spectrum and depend on other types of lighting. Farmers or growers often use reflectors to direct as much of the HPS light toward the plants as possible.


While one 400-watt HPS bulb costs about $75, as of 2010, it can last for up to two years, illustrating how cost efficient HPS lights can be. It would take 10 54-watt tube fluorescent lights at $20 each to give a comparable light. However, because HPS lights are also more efficient they cost less to operate. Greenhouse growers use natural light for growing their plants but supplement their lighting with HPS lights during flowering and fruiting stages of the plant.


HPS lights must be used in conjunction with other equipment. The electrical current to the HPS bulb is controlled by a ballast. Differences in temperature and high humidity are some of the factors that can affect the ballast's operation, so it must be checked regularly. Also, because these lights operate at very high temperatures, they require a cooling system.

Combination Lights

When plants are young and still in the vegetative stage, HPS lights are not usually used or are used in combination with metal halide lights. Metal halide lights give off light in the blue part of the spectrum, which is the type of light growing plants require. Growers also use Light Emitting Diodes (LED) in combination with HPS lights because HPS require additional equipment for cooling. LED lights glow cool and are lightweight and economical.


Plants grown under HPS light can grow leggy. They often look pale and starved of nitrogen, but in fact they are healthy regardless of the way they look. HPS lights also get extremely hot and can burn if they are placed too close to the plants. Workers should also take precautions such as wearing protective clothing and glasses because HPS lamps emit ultraviolet light. Good ventilation is a must to keep the plants healthy.

Keywords: high-pressure sodium lamps, HPS lights, growing indoor plants

About this Author

Beverley Burgess Bell has been a professional freelance writer since 1986. She has worked for Medigram, a medical poster, and Rodar Publications. She also was editor of "Epilepsy," Canada's national newsletter and wrote for various publications including "Future Health." She has a Bachelor of Arts in journalism from Concordia University in Montreal.

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