Hi, just wondering, what's the optimum lumens per square foot of plants? I know the minimum is 3500ish, but is there a point where it levels off, like a bell curve? I've got a pc case as my growspace, it's got an approximate volume of a cubic foot. Thanks!
In a pc grow you will either run out of room or have too much heat before you are able to get enough lumens going.
Depends on what type of light. Plants don't give a shit about lumens, they want photons in the PAR range mainly. Botanists use PPFD (Photosynthetic Photon Flux Density) which is quantified as µmol photons/m2/second. What does this mean? Without an expensive PPF meter, you need to use W/sq.ft. as a reference and hopefully most of that photon energy comes in the PAR range. Because photosynthesis is a quantum process, PPFD is generally used by plant biologists, not lumens.
Not true. Go with LEDs. Do your homework and you will be happy. Low heat, good nugs. Don't believe me? check some PC grows in other forums. I have one going currently just about to flip to flower. 27 Watts of LED in .56sq.ft. PC case. Hopefully I get 1 or more grams per watt.
^Yeah, blah blah -- all true, but totally misses the point. MJ growers use only certain kinds of light (or they should anyway) and the relationship between PAR and lumens is fairly well known with these lights. We don't need to make this too complicated as long as we are talking about lighting that is known to be focused in the range usable to MJ. And since lumens is a readily available metric while PAR is not, it's fine to talk about lumens as long as we're talking HPS, MH, and CFL/fluros targeted in the 2700k and 6500k ranges. To the OP's question, you should target a minimum of 5,000 lumens per sq foot. As Lay Low said, full sun is around 10,000 lumens. True there have been some successful grows with LED, but there still are far too many unsuccessful ones for me to bet on this technology yet. My assessment is that LED could be the wave of the future but it's just not yet ready for prime time. FYI flowering is where LEDs tend to fall behind.
The point is lumens aren't what grows plants. But if you must use lumens to judge your light then go ahead. How do you know LED can't be used in a PC case? We aren't talking about 2000 Watts worth, just a small grow.
Toastybiz's light game in on point. I agree with all of this. PAR is useless to talk about because all bulbs are not rated in PAR, and scientists don't even agree as to what the correct PAR range even is. Like he said we already know the which lights have the most PAR watts, so then no other info about PAR is needed. All you need to know is which lights to use, and that is common knowledge among growers. After that you just go by lumens because you have no choice since that is what the lamps are rated with generally. There is nothing else to go by. Agreed again. The only time I would ever consider going with LED is in some kind of micro grow. They still don't come close to HPS for flowering. Someday perhaps they will, but currently they have a long ways to go. Personally I think plasma lighting has much more potential to revolutionize horticultural lighting than LED does.
It is looking that way, that by the time LEDs really do get to be fully reliable for consistently strong yields that plasma will have surpassed them. But that's all in the future, my crystal ball is a little fuzzy. The tried-and-true in the present day remain HPS, MH, and CFL/fluoros.