One of the challenges for a beginner—or even for the experienced grower who’s about to upgrade their operation—is picking the right lighting system. HID lamps are still the most common and affordable option for an indoor plantation or small commercial operation. Assuming one makes the choice to go with these high-intensity discharge lamps, which means MH lamps for the veg stage and HPS lamps for bloom, the grower is probably aware that a specific power supply unit is needed too.

HID lamps are very efficient at turning electricity into light. They produce light by means of an electric arc ignited between the electrodes, which requires precise current calibration, with different current intensities in the start-up phase and during normal operation. Different gases inside the bulbs provide different light spectra. That’s why we switch from MH (metal halide) lamps in the vegetative phase to HPS (high-pressure sodium) when it’s time for blooming. A ballast provides power to the lamp by regulating voltage, preventing HID lights from drawing too much current all at once. It also delivers stable electrical power despite normal line fluctuations. Importantly, the electrical output of the ballast must match the requirements of the lamp.


There are two main types of ballasts that suit the needs of indoor cannabis growers. Old-school magnetic ballasts have transformer coils and a capacitor starter in charge to regulate the voltage. They have been around for decades and their main advantage is the low price. Unfortunately, they dissipate a lot of energy in the form of heat, resulting in higher power consumption and temperatures in the growing area.

The digital technology integrated in the new generation of electronic ballasts makes them smaller, able to operate at a lower temperature, and much more efficient than electromagnetic devices. The built-in features of these ballasts usually allow the grower to control and regulate, in real-time, the power that the ballast sends to the lamp. Electronic ballasts don’t emit vibrations, and they avoid the typical flickering induced by magnetic ballasts. The stable power flow they provide also increases the lifetime of the HID lamps.

Ballasts for Cannabis Cultivation


Both the performance and the lifetime of the bulb depend in part on the quality of the ballast used. If the grower wants to hand-pick bulbs, hoods, and ballasts instead of buying a whole lighting kit, they will need to ensure that the lamp and ballast are compatible. Also, since the market is flooded with low-quality components, it’s important to purchase all growing equipment, particularly electrical devices, from reputable suppliers to avoid any issues, some of which could be potentially catastrophic. Some of the most reliable ballast manufacturers include Gavita, Sonlight, Lumatek, Adjust-A-Wings, Lumii, and Nanolux.

In an HID system, the ballast is connected to the power socket while its two output cables are connected to the bulb holder, which is usually incorporated in reflectors or cooling tubes. Don’t forget to respect the polarity and to connect the ground cable too! Many new ballasts come with the wiring system already installed.

Ballasts should be kept out of the growing space—particularly the hot electromagnetic models—and off the ground to reduce the risk of short circuit and damage by water and humidity. A good idea is to hang them high on a wall or panel that can resist heat, together with all the rest of the electrical plugs and switches.

Electronic dimmable ballasts allow growers to set different power levels, which can be convenient when you have to comply with plants’ needs during different stages of growth, and also when it becomes mandatory to reduce heat in the grow room during summer. Many new ballasts also have a “soft start” function that simulates the natural sunrise, and a switch that allows growers to use the same ballast for different circuits. The switch is useful when you want to operate two different grow rooms with alternating night and day periods using a single ballast.

As a final note, you should eventually consider that ballasts emanate radio frequency interference (RFI), which can interfere with radio transmissions and can therefore be detected. Amateur radio operators tested several ballasts for RFI, finding that one single ballast can cause radio interference extending up to 700 metres. They also found that some models are more shielded than others, and that a common nickel-copper RF shielding can effectively contain radio frequency emissions from a grow light ballast.


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