Grow Light Ballasts
Metal Halide (MH) and High Pressure Sodium (HPS) lights require a remote ballast to work. When building your own plant grow light, it’s important to match the ballast with the wattage of the bulb you will be using. You must also match the type of light (MH or HPS) you’re looking for with the ballast. For example, a 400 watt HPS bulb will only work with a 400 watt HPS ballast (or 400 watt convertible ballast). A Metal Halide bulb must be used with MH ballasts (or convertible ballasts) of the same wattage.
Note: Digital ballasts (Quantum, Phantom, etc.) will work with both MH and HPS lamps of the same wattage.
Grow Light Bulbs
Because of their color spectrums and high light output (wattage), Metal Halide and High Pressure Sodium bulbs are the most popular indoor plant lights available.
Metal Halide Lamps produce a more natural color spectrum of light, with more blue and violet light rays than HPS lights. MH lights encourage vegetative growth and “bushiness” while discouraging upward growth. This is the light to use in the vegetative phase of plant growth, or when starting seeds and cuttings.
Used primarily in the flowering cycle of a plant’s life, HPS Lamps emit a yellow/orange/red light that is typical of autumn’s harvest sun. Many indoor gardeners switch to high pressure sodium lamps in the later stages of a plant’s life to induce flowering, budding or fruiting.
Conversion Bulbs make it possible to run a metal halide bulb from your high pressure sodium ballast or a HPS bulb from your MH ballast. The most popular conversion bulbs by far are sodium conversion bulbs, which allow growers to have the sodium spectrum while still using a metal halide system. Although not as bright as regular HPS lamps, conversion bulbs are more economical than buying two complete systems. (Note: This type of bulb is not necessary when using a digital ballast.)
Grow Light Reflectors
Reflective hoods are essential to ensure that all the light is reflected toward the plants and not wasted throughout the room. The more “reflectivity” a hood can provide, the more effective it will be. In fact, gardeners who use the most efficient reflective hoods can harvest up to twice as much produce as those who don’t. DON’T skimp on your hood — it’s all about light output, right?
Hope this helps!