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I will build a grow light system from LED lights for a 1m x 2m square area. I am planning to grow 6 plants (vegetables) in that area. I am a little tight in terms of budget. So I want to find cheapest option while obtaining enough result.

My plan is to build a grid system made from LEDs.

I know that I should obtain full spectrum by using different wavelengths, but I can't decide how many watts I should obtain. According to my research I should get 1200 watts for 2 meter square. But it really costs me too much.

So I want to ask exactly how many watts do I need for that kind of setup.

  • Not sure if this is a duplicate, but it will be useful if nothing else: gardening.stackexchange.com/questions/5977/… – GardenerJ Dec 6 '16 at 20:40
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    You don't actually need full-spectrum - LED plant lights are made which concentrate the light output into bands most useful for plant growth, with different curves for vegetative (lettuce, etc) and flowering/fruiting plants. As with florescent "grow lights" the result tends to look a bit purplish (plants don't use green light, which is why they look green, since they reflect it.) – Ecnerwal Dec 6 '16 at 22:31
  • A few observations - The exact light colors you need will depend on what you are planting but you don't need full spectrum. Plants need blue and red mainly, green does very little for them. Watts is irrelevant, PAR is analogous to lumens but for frequencies the plants use. The closer to the plant the lights are, the less wattage you need (6 smaller lights you can lower will be cheaper then 1 or 2 big lights which don't focus light). Sometimes using strips of lights weaved through the plants can help. 1200 watts generates an awful lot of heat). – davidgo Dec 7 '16 at 21:33
  • Rule of thumb in growing - 1% more light = 1% more growth, so more light will get your plants growing faster. Sunlight is the gold standard - if practical (legal?), you can reduce your lighting requirements a lot buy using sunlight when its there. Typical sunlight is between 100 (overcast) and 1000 (sunny day) watts per square meter, or extremely roughly 1000 to 10000 lumen/sqm – davidgo Dec 7 '16 at 21:40
  • @davidgo Isn't PAR an absolute measure not adjusted for frequencies that are not readily absorbed by plants? All these units are a bit useless if a green LED will get the same number as a red one. – user10810 Dec 7 '16 at 23:20
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LEDs produce more light for the watt, so they should probably work out to be the cheapest solution in the long run.

As far as LED grow lights are concerned, I did some price checking and found that you can't cheat with how much light you get for your buck. $1k+ lights just happen to have that many diodes/higher power diodes compared to the $10 ones. Higher end stuff will be better built and marginally more efficient but that doesn't matter when you can't afford to buy them.

What you can do to improve your cost performance ratio is to buy more of the cheaper lights and build them into a dome so that each plant gets more light. It's less convenient than having a single small sun on top of your plants, but it works.

I've been growing a few small plants covering a square meter on about 75w of red-blue LEDs using this technique. After two months, none of them, not even the seedlings, show any sign of light deficiency and the tomatoes seem to love it to the point they might become too large for my current set-up. I was planning to buy more lights but it looks like it won't be necessary. I'm not trying to get any fruit, or exceptional growth though, this is just for overwintering tender plants.

You might really need 10x what I'm using, however, I think you should look at volume rather than surface. A two meters tall herb doesn't need the same amount of light a lettuce does and most of the information you will see around is about growing herbs.

The downside to LEDs is that they produce less heat than other light sources so you have to heat the plants separately if your indoor temperatures get too low.

That and you have to cover every window or your neighbors will think you are growing herbs or running a house of ill repute.

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This is a great subject. Forget LED's. Wimpy. The plants care about lumens, your wallet cares about watts.

The sun has approximately 1KW per square meter. LED's aren't going to work. So here are some suggestions because we were constrained by budget and this is what we've done

Get an 8 bulb (T-5) fixture that takes very little power. No ballast is needed It will put out 40,000 lumens at 500 watts. This is the lowest cheapest system we found to use and used successfully to grow vegies from seed to harvest. Cost; $250 and came with 8 bulbs in the blue spectrum. We purchased 8 bulbs later to get the red spectrum and reproductive growth going; cost about a hundred bucks...that you don't have to spend until you get your plants through their vegetative stage, no matter what kind of plant. The red spectrum triggers reproductive growth for tomatoes the blue would be fine for leafy greens the entire time.

We finally were able to afford a grow light fixture with ballast , comes with 2 bulbs, a metal halide bulb which is in the blue spectrum and a second bulb, high pressure sodium (hps) that functions in the red spectrum. One bulb at a time depending on your project, we've had ours for 2 years full time use and still fine. 2 bulbs, the fixture the ballast for $250 to $350. We got ours on some special deal at $250. This provides LUMENS 80K for metal halide and 95K for the high pressure sodium.

Look up HTG Supply for lighting, we got our best deals through this company.

One other answer that would follow your idea of a grid would be to use CFL's Compact Fluorescent Light in place of your LEDs. (Those spiraled light fixtures we use now in place of the incandescent bulbs). The one problem you will have with those is the fixture or lack thereof. The light goes everywhere not just the plants so a lot of energy and light is wasted. LED's, we TRIED using them and just not enough light period. Turned out to be a joke.

You'd need 6 CFL bulbs 300 watt full spectrum spaced each meter, paint the walls white and somehow devise a reflector for the bulbs. Each bulb costs $30 to $50 bucks each X 6 = $180-$300, not including your fixtures, the wiring, the need for a dedicated breaker in your electrical panel, the paint and I kid you not the fans you have to have. A way to get fresh air into your system, dirty air (full of O2) out of the system and a heater! Timers, drainage? Fans to move the air forcefully not used for cooling to prevent the higher humidity promoting fungus. You'll end up eventually purchasing a humidifier. The best fertilizer you can afford and understand or go Osmocote for safety and expense. Soil, potting soil, sterilized soil isn't expensive but if you don't use potting soil I wouldn't bother getting lights. Drainage for your pots, properly sterilized pots with holes, sized for the plants. You never put a tiny little plant or start in a big pot. You have to up pot at least 3 or 4 times using potting soil. So the expense in tiny pots 2-3" max for growing from seed to 4 and 6" pots to at least one gallon, or two gallon or five gallons depending on the type of plant, rate of growth. Never bring garden soil into your system, never bring a plant someone has given you. Purchased starts are ok but still a risk. How proficient are you at growing vegetables, plants in a controlled sequestered indoor application? Expect failures at the beginning but LED lighting is not going to work. Go get Shane Smith's greenhouse gardening AND Jorge Cervantes Cannabis Encyclopedia. The best most detailed books you should have and read if you want success of any kind. Hope this helps, please let me know if you need clarification on any of this!!

Go get Jorge Cervantes' The Cannabis Encyclopedia. Everything you need to know about light and plants is in Chapter 17, pages, 253 through 302. This is so well done...oh he gets into PAR big time, how expensive it is just to get a number, turns out it is a pretty useless number, like you said. The most important numbers are the LUMENS (intensity) and CRI (frequency). They have equivalent temperature codes (degrees Kelvin).

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    Plants don't care about lumens, actually - lumens are based on the human eye response curve, which peaks in the yellow-green (which plants don't use) - Photosythentic Active Radiation (PAR) is what plants care about, but good luck finding that figure on many lights. – Ecnerwal Dec 6 '16 at 22:34
  • So what do you use, or recommend? This is a subject I get help with from my Electrical Engineer hubby. The two of us have been learning as we go but HE was the one to come up with Plants care about lumens...makes sense to me but this is how I learn, to delve into something I know little about except from experience. He knows electricity and lighting and now has 4 years of experience with plants and artificial light. PAR huh? Gotta go look this up because we are talking about recreating the sun's light for photosynthesis indoors. That we've done with good success... – stormy Dec 6 '16 at 22:57
  • Well, if one can't find THAT PAR information, I do know that lumens are far more closely related than wattage. Interesting. Thanks, Ecnerwal! – stormy Dec 6 '16 at 22:58
  • PAR is also tough to measure and expensive. 3 things are necessary to know to be able to help this guy; Lumens are little packets of light and are the INTENSITY of the light source. PAR is a measure of the received energy with the right frequencies that the plant needs for photosynthesis. The third is photo period. For instance; Green is not involved in photosynthesis, Reds and Blues are used. All of them are part of the visible light spectrum. Depending on individual plant needs part of the light will be wasted. Plants need intensity! – stormy Dec 7 '16 at 1:20

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