Your lighting choice is the first thing that will determine the type of ballast you need for your greenhouse lighting system. High Intensity Discharge (HID) lamps like metal halide or high-pressure sodium. Grow lights receive electrical currents through a ballast that makes sure they run on the appropriate voltage from an outlet (total wattage needed by the ballast and lamp are called the input watts). HID ballasts can come with reflectors and fans or without, so you will want to pay attention to the ballast's features and design.

LED grow lights have gained popularity because they run cooler and can be placed closer to the canopy of a crop. LEDs are also more energy-efficient than HID lamps. LED lamps consist of many small lights (diodes) in a grid, called an array. The LED grow light will have a driver that functions like a ballast and regulates the input power. The driver also protects the diodes from voltage fluctuations as they heat up and age. No additional ballast is needed for this style of grow light.

Fluorescent grow lights plug into a ballast that regulates the electrical current flowing into the bulb to ensure it is supplied at the correct voltage. There are three main types of fluorescent grow light ballasts: preheat operation, rapid start operation, and instant start operation. Preheat operation is used mainly for bulbs under 30 watts and is more energy-efficient than rapid-start operation. Rapid start operation is the most popular fluorescent ballast operation mode. This is the mode where the stereotypical fluorescent light flicker occurs. Using the preheat and instant start modes may lower the lifespan of the ballast.

There are several different types of grow lights for greenhouse growers to select from. In order to select proper lighting, it is important to consider PAR, PPFD, DLI, and other factors that describe a light’s electrical use and lifespan. Some grow lights draw large currents that require outlets that can put out more amperes. It is very important to be sure that lighting equipment is compatible with the outlet capacity! HID lamps and fluorescent bulbs must also be compatible with the ballast where they are screwed in.

Magnetic ballasts have an iron core. They are heavy, inefficient, and produce a buzzing noise. Digital ballasts are more expensive than magnetic but are more energy efficient. Ballast with built-in cooling fans or exposed ballast designs are helpful since HID lamps produce a lot of heat.

Air-cooled ballast hoods are sealed reflective hoods that connect to ducts equipped with an exhaust fan to move out the heat. Water-cooled hoods are more efficient than air-cooled hoods. They allow growers to move lamps closer to the plant canopy. Water used for cooling this type of ballast is chilled in a reservoir above the sealed reflective hood. Then it is pumped through, transporting heat away from the lamp.

Diagram of an HPS Lamp Ballast System by Sakurambo CC-BY-SA-3.0