How many watts per square feet for marijuana grow room?

I’m growing marijuana using a system of about 65 watts per square foot (psf). These lights are air-cooled and on light movers. I had the notion to spread the marijuana plants out over a larger area so they could get about 50 watts psf. I talked to one expert who told me that I should switch to 600-watt HPS lamps. Is that feasible or should I just stick with the 1,000-watt lamps? If the buds increase in size, will they lose their potency and/or become leafier?

If you’re looking to add more space, it’s best to add more lighting to the marijuana. Replacing 65 watts psf with 50 watts psf—a 23% reduction in light—will impinge on growth and produce leafier, fluffier buds. Although they might have the same total weight as the buds that had brighter light to work with, they will still be looser and of a much lower quality.

When marijuana is grown under a more intense lighting regimen, the plants will produce denser, heavier buds. These will, of course, be better than buds grown under less intense lighting. Bud density comes from a large amount of flowers growing in a small area. The flowers squeeze together and become densely packed making for a much more potent product in the long run.

It’s likely that the expert recommended using 600-watt lamps instead of 1,000’s because of their somewhat higher light-producing efficiency. They do maintain certain drawbacks, though. It is harder to deliver intense light to the marijuana plants when using lamps with smaller wattages. You would need more fixtures and bulbs which would end up costing you more money. On the other hand, a larger amount of smaller wattage lamps tends to distribute light more evenly to the garden.


A rule of thumb when using HID lamps This is the amount of SF’ each size HID lamp can cover. This is without the use of a light mover.

250w can cover
400w can cover from:
3’x3’-4’x4’ especially in a tent
600w will cover:
1000w HID cover 6’x8’ of intense light.

If I had the adequate ventilation to use 1000w. That would be my choice, but many growers swear by the smaller but potent 600w HiD