Lighting space

Are two 1000-watt metal halide lamps on light rails enough light for a grow room that is 3 meters wide and 4.4 meters long?
Brisbane, Australia

Your grow room is 13 square meters (about 120 square feet). A 1000-watt metal halide is most efficient at lighting a space of about 1.5 meters (13 square feet). The two lamps will light an area of 3 square meters, which is 1.5 x 2 meters.

If the room was maximized it would have two planting areas. Each space would be 4.4 meters long and 1 meter wide, with a meter wide walkway between the gardens. Each garden would use three 1000-watt lamps.

Readers with grow questions (or answers) should send them to Ed at: Ask Ed, PMB 147, 530 Divisadero St., San Francisco, California 94117, USA
You can also email Ed at [email protected], and send queries via his website at
All featured questions will be rewarded with a copy of Ed’s The Big Book of Buds from Quick Trading.
Sorry, Ed cannot send personal replies to your questions.

I would change over to high pressure sodium (HPS) conversion bulbs to get the most efficient use of the lighting. Any new ballasts should all be HPS.

If you were running all the lights at the same time they would produce more than 20,000 BTU’s of heat. Air-cooled reflectors keep the lights cool using cool air, enclosed in reflectors and tubing so that the heat never gets into the room. This eliminates more than half the heat the lights generate.

Keeping the ballasts in an area separate from the garden will also eliminate thousands of BTU’s. The ballast area can be cooled using separate intake and outtake fans.

Devising a curtain system would allow you to run one half of the garden at a time during flowering. Only half the heat would be generated at any time, so it would be easier to keep the room cool.