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lumens for growing weed

Lumens for growing weed

So while a 1,000-watt bulb may seem plenty sufficient for a 4’ x 4’, it will be too much light. In a 4’ x 4’ x 8’ tent with no exhaust, a 1,000-watt bulb has the power to raise the temperature nearly 25 degrees in no time. That means 68°F can climb to over 90°F! Even with ample exhaust, you’d be hard pressed to keep temps below 80°F.

Most plant leaves do their best conversion with sunlight between 3,000 and 4,000 lumens per square foot. Let’s assume, on average, that a 1,000-watt high-pressure sodium (HPS) bulb has an output of 100,000 lumens. At a leaf’s peak efficiency of 4,000 lumens per square foot, that leaves an optimal coverage area of 25 square feet—or a 5’ x 5’ footprint—for a 1,000-watt bulb.

A good example of this is the fact that many bulbs are still marketed using “lumens” as a selling point. While lumens are a measurement of light quantity, it is not an appropriate term for horticultural purposes.

Of course, bulb manufacturers and garden shop sales people will tell you a 1,000-watt bulb covers anywhere from 6’ x 6’ t0 8’ x 8’, but that is not based on photosynthetic processes but rather on physical light coverage (hence the use of lumens and not PAR).

Greetings to you, Nico!
I have searched the web and noticed that you are the guy to ask about indoor lighting for cannabis horticulture. My question is rather simple, I think: In terms of lumens, what light output do I need to grow a plant or two successfully in my home? I have a small bedroom and am thinking of using a ’ x 4’ or 4’ x 8’ grow tent? Any suggestions on bulb types and strength would be helpful! Many thanks & good luck to you! — Jonathan V. via the mailbag at [email protected]

This 4′ x 8′ grow tent uses two 1,000-watt HPS bulbs, but must air cool the lamps to keep temps down. (Photo by Nico Escondido)

The solution is simple: a 400-watt or 600-watt will serve you and your plants much better. A 400-watt HPS puts out approximately 50,000 lumens. With a 16-square foot footprint in a 4’ x 4’, that’s 3,125 lumens per sq. foot. A 600-watter is roughly 80,000 lumens, giving 5,000 lumens per sq. foot in the same tent.

LEDs could pose an alternative in the future, but right now, LED companies like this one are going belly-up after coming to market with a $1,400 price tag. (Photo by Nico Escondido)

Thank you, Jonathan, for reading and writing in with an excellent question!

LEDs could pose an alternative in the future, but right now, LED companies like this one are going belly-up after coming to market with a $1,400 price tag. (Photo by Nico Escondido)

Lumens are the amount of light a bulb provides. Essentially, lumens mean brightness. The higher the amount of lumens, the brighter the light that will be achieved. Plants, especially cannabis plants, require adequate light to grow. Typically, one cannabis plant needs at least 2,500 to 3,000 lumens.

Maximum Yield Explains Lumens (lm)

Ideally, a marijuana plant should have 4,500 lumens to ensure maximum growth. A 4,500-lumen bulb will cover a 3×3-foot space with adequate lighting.

Most standard fluorescent tubes produce 3,000 to 3,300 lumens per tube. There are various tricks that a cannabis grower can do to increase the lumens of a grow light, such as placing a metal or foil reflector behind the bulb or tube to reflect even more light down onto the plant. This trick increases the amount of lumens generated by the light source that reach the plants.