Watts per foot question

Somewhere between 20 and 60 right? But what if space isn't a concern? For example, 20 watts per square feet over a 9 foot area, or 60 watts per square foot over a 3 foot area?

In considering the question assume the light source was consistent over the grow area, not "well you can get 1 lamp over a 3x3' area". Thinking LEDs rather than a single point light source. Hope that makes sense.

Or same example over a larger area: 20 watts per foot over a 3x9' area -vs- 60 watts per foot over a 3x3' area. Which would yield more?

Rahz said:

Thinking LEDs rather than a single point light source.

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Depends on the efficiency of the LED. If you buy Chinese imports (cheap or expensive rebranded lights), you'll need over 30w sq. ft. A lot of owners of such lights go to 40 and above. If you invest in more efficient LEDs (Area51, Onyx, Hans, Apache or those Cree incadescent replacements at Home Depot), you need 20-25w sq ft.

Watts per cu. ft might also be a way to look at it. If you grow tall plants you might benefit from side lighting.

Thanks for the reply but it's not exactly addressing the gist of the question, though I do appreciate the validity of your response.

Assume the LEDs were efficient, and could be spread out in any configuration (think DIY rather than a consumer product). Going by your figures let's say we were using 25 watts per foot over a 3x3 area. How would the yield be affected by using the same power evenly distributed over a 3x6 area (12.5 watts per foot).

See where I'm going with the question?

Rahz said:

How would the yield be affected by using the same power evenly distributed over a 3x6 area (12.5 watts per foot).

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I think I understand what you mean. An example is Area 51's RW-150. Those considering the light are often encouraged to buy two RW-75s. It's the same power draw, but the two light sources allow for slightly more coverage.

You need to get the attention of @stardustsailor . He's a big proponent of surrounding a plant in multiple sources of light. He put together air-cooled LEDs under the name of Astir lighting. There is a huge thread where he talked about it. (<Link).

I have 2cxas running 105W each in a 2x4 tent. should i add some more lighting?

A $30 light meter will answer the question.

actually that would make me ask another question.. how many lumens per sqft would i need?

right now they put out 23.500 lumens

Depends what stage you are in. Its better to measure in foot candles rather than lumens when it come to measuring the light. In veg i go 24fc in the corners and 35fc-50fc+ Diring bloom it 60fc min for me and in some spots 90fc or more. Just hold the sensor at canopy level to measue.

Edit. The meter says the 2 digit numbers listed above but it is multiplied by whatever you set it on. For example the 35 fc is actually 35,000fc and so forth.