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LED newbie, need advice on wattage, setup for plants, etc.

Posted by rredbbeard SE CT USA/zone 6 ( on
Sat, Aug 2, 14 at 20:13

I'm setting up a basement area where many of my plants will go this winter, and these plants require approximately 80-90% natural sunlight, similar to the intensity at 30�S latitude in autumn. I purchased a large screw-in LED directional bulb/fixture, 21 watts with output of 1150 lumens.

My questions are: how far from the top of the plants should this bulb be, and what square footage of plants can I put under the light? Most of the plants that will go here will be succulents--aloe, albuca, oxalis obtusa, stapeliads, etc., basically south african species.

I have several smaller LED red/blue 2.2w bulbs that will also be used.

Is there a 'rule of thumb' to calculate LED wattage per square foot required at a given height, to produce a desired % of natural sunlight?

If you're using LED's exclusively for plants with high light requirements, I'd really like to hear about your excruciating detail, 'natch!


--Rick in CT

Follow-Up Postings:

RE: LED newbie, need advice on wattage, setup for plants, etc.

I am unfortunately in a hospital waiting room, so I can only give general rules of thumb.

You need to know two things for indoor lighting. How much power do you have, and how well can you deal with heat.

How much power you have is right in the specs, although I assume you're missing part of the lamp spec. If it really only tells you lumens, they mean one foot distance. However, with a fixture, I would expect them to tell you lumens PER SQ FT, at some distance. See if you can find a reference to distance in your manual.

The short answer is you need to have enough light to cover the square footage of plants you have, no one agrees what percentage of sunlight you need, and temperature and ventilation starts to really matter when your light gets strong. You want your plants as close as they can be without burning them, assuming you cover the entire growing space.

CFLS, LED, and Flourescent lights can touch plants with good hydration and ventilation. HPS can burn from a foot at higher power.

If you use your smartphone with a light meter app, you can get a rough estimate of the available light, keeping in mind it has to be the right color spectrum. You are shooting for somewhere in 7,000 to 15,000 lumens range per square foot. That means your fixture probably needs to be about three to six inches for vigorous growth. You could keep vegetative plants happy with more distance.

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