HPS or MH light for flowering and vegetation of marijuana


I bought a 400-watt metal halide (MH) lamp, which the salesman said could be used for flowering and vegetative growth of marijuana. But, my friend indicated that MH lamps won’t do much good and I should just use a high pressure sodium lamp (HPS) instead. And what’s better: an enhanced spectrum HPS lamp like the Son Agro 430-watt bulb or a regular HPS that emits more light in the blue spectrum?

MH lamps have more blue light and less red light than HPS. HPS lamps create more light in general than MH lamps and more light in the red spectrum, which is more beneficial to the rate of photosynthesis. Red light also assists in flower development.

The only real reason to use an MH lamp instead of an HPS is to stay away from any suspicion that strange-colored lights might bring. MH lamps at any stage of growth are genuine wastes of time and money. More total light and more useable light comes from HPS lamps, and marijuana plants tend to grow faster using HPS lamps by themselves.

Plants don’t really benefit from the extra blue light provided by the Son Agro. Despite the fact that marijuana plants do use blue light for photosynthesis, it doesn’t really increase production when compared to red light. Rooms that have mixed MH and HPS lights tend to have some plants that didn’t develop fully and some plants that did. Usually, the plants sitting under exclusively HPS light yield significantly more than plants under a mixture of the two light or MH light by itself. You could definitely see the “wave effect.”

To fix your ballast problem, just replace the MH bulb with an MH-to-HPS conversion lamp. The bulb will fit into your system without having to scrap the whole thing and will emit light at an HPS spectrum.