I often read that when choosing lighting for a grow room one should aim for a minimum of 50w per square foot. I was curious what the impact is if more or less light is used. If, for example, 40w per square foot is used will the plants grow too slow making it a waste of electricity, or will it simply not reach all parts of the plant. What if it is 30-40w per square foot, but the entire tent is not used, how will this impact the plant. Conversely, if I have 80w per sqaure foot (assuming heat is not an issue) will the plant grow that much/better faster? Any information would be appreciated. Thanks
50w per square foot?
- Thread starter kesaber
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good question, the watt per square foot is just a rule of thumb and really only applies if you are comparing hid to hid or cfl to cfl or led to led. Most of us don't have one light per square foot so then you get to talking about total coverage. And yes, there is no such thing as too much artificial light, the only constraints being heat and electricity and initial cost. Not enough light produces low yield and sometimes low quality.
But once you start talking "usable" light, there is no end to the debate
dandyrandy
Well-Known Member
I use 900w (9 vero 29's) at the last month or so of bloom. I seem to get better lower bud development. It's a 40x46 inch area. Usually run 600 until the last month.
for instance, I can grow good pot in a 2x2 space with just a 200w cfl. For me that is just one plant in a large container. I tried growing two plants in smaller containers, but it's just not enough light for me. I wouldn't be comfortable replacing my 200w cfl with any hid less than 400w. Although I do use 220w led in my other closet, and same thing, good for one plant in 2x2, but no more.
But the question was more about how light affects plants. Quite a bit! That's why most home growers bend or top their plants to create an even canopy which eliminates the need for deep light penetration. But no, more light won't create some new fast growing monster. Plants with insufficient light tend to have looser buds and wider spaced nodes.
But the question was more about how light affects plants. Quite a bit! That's why most home growers bend or top their plants to create an even canopy which eliminates the need for deep light penetration. But no, more light won't create some new fast growing monster. Plants with insufficient light tend to have looser buds and wider spaced nodes.
bicit
Well-Known Member
Depends on the efficiency of the lighting setup. Slightly less light wouldn't be a waste, growth would just be slower. Too much light will result in bleaching and burnt plants.
50w/ft^2 is a good rule of thumb with most light sources. Cfl would need slightly more, high efficiency cobs slightly less. It is a very broad sense of things though.
What sort of lighting arrangement do you have in mind?
Over 1500 umoles/m^2 is the point of diminishing returns according to betatestteam on icmag. Supra runs 750 umols in his garden for quality purposes.
Lots of area for debate on ideal. Start with 40-50 and go from there.
50w/ft^2 is a good rule of thumb with most light sources. Cfl would need slightly more, high efficiency cobs slightly less. It is a very broad sense of things though.
What sort of lighting arrangement do you have in mind?
Im going to say now that you are very wrong. With artificial lighting, esp with hid and cob leds it is really easy to oversaturate a plant with light.
Over 1500 umoles/m^2 is the point of diminishing returns according to betatestteam on icmag. Supra runs 750 umols in his garden for quality purposes.
Lots of area for debate on ideal. Start with 40-50 and go from there.
I'll leave that to you experts. I was just trying to help a guy figure out the deal. Like I said, if it doesn't cost too much to buy, and it doesn't use too much electricity, and it doesn't create too much heat, it is probably not too much light.
captainmorgan
Well-Known Member
With the high end COBs,30 watts a sq/ft going to the COBs will kick butt.
churchhaze
Well-Known Member
Like bicit said, it depends on efficiency. It also depends on the height of the plants you're growing.
For 2-3 foot tall plants, 14W/sqft PAR (radiant power between 400nm-700nm) is a good amount of light.
With a 35% efficient broad spectrum lamp (like 600W hps), that's about 40W/sqft (14W/0.35 = 40W).
With a 40% efficient broad spectrum lamp, that's about 35W/sqft. (14W/0.40 = 35W)
With a 50% efficient broad spectrum lamp, that's about 28W/sqft (14W/0.50 = 28W)
For 2-3 foot tall plants, 14W/sqft PAR (radiant power between 400nm-700nm) is a good amount of light.
With a 35% efficient broad spectrum lamp (like 600W hps), that's about 40W/sqft (14W/0.35 = 40W).
With a 40% efficient broad spectrum lamp, that's about 35W/sqft. (14W/0.40 = 35W)
With a 50% efficient broad spectrum lamp, that's about 28W/sqft (14W/0.50 = 28W)
JimmyIndica
Well-Known Member
Height of the plant-optics being used-how hard u runnin em-height of fixture from canopy- all variables that are all different with every grower! This thread is bound too start arguments? Someone growing 4 footers vs someone growing with screen {topsonly} that doesn't need penetration can get away with softer running lower wattage cobs without optics! ME! I like making em blow up! I use 40-45persquare
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JimmyIndica
Well-Known Member
2x2 -200watts although thats probably too much by others standards
I figure, to cover 2x2, you need 200w cfl, or 220 led, or 400w hid. Anything less is not enough for me.
AquariusPanta
Well-Known Member
Seeing as how Cree and Bridgelux Vero COBS are far more efficient than CFL when ran at reasonable currents, it would make sense that less COB watts would be required to grow and show similar or better results in comparison to CFL and HID.
and even then, I have my doubts about cfl or led compared to hid. For years growers have been using 400w mh/hps to cover 2x2 or 600w mh/hps to cover 4x4 with great results. So we already know that works. CFL and LED are still experimental and nobody knows for sure what their limits are. Like I said, the debate goes beyond watts and gets into par and usable light. 50 watts per square foot is a good starting place for mh/hps. But you know, we always think we can do better.
Are you serious? Do you bother to read the threads on this forum about LEDs (and not the red/blue LED lamps)? There are many of us putting out successful grows with COBS that are just as good of quality (if not better) and the weight is there. I just put out 1.21g/watt in a 10sq ft space with 400w of CXB3070 for a total of 487g. There is no way a 400w HPS could hit that and I would think that a 600w would have trouble. I ran a 1000w HPS in the same area and my best yield was 588g and while I do believe that 1000w was wayyyy too much for the area, I dont believe a 600w could have matched that.
a mongo frog
Well-Known Member
Flagg420
Well-Known Member
meh, size doesn't matter, lol... (grow area) Go as powerful as your cooling permits, more power isn't so much for coverage, as for penetration.... After stretch n bud formation, only the outside of the plants getting light under CFL desk lamp bulbs.... a 1000w HPS will give light to bud sights 12-18inches deep into the foliage... 
yeah, but we are small growers in a small space, and we LST, so we don't need any penetration. Our canopies are as smooth as a baby's bottom.meh, size doesn't matter, lol... (grow area) Go as powerful as your cooling permits, more power isn't so much for coverage, as for penetration.... After stretch n bud formation, only the outside of the plants getting light under CFL desk lamp bulbs.... a 1000w HPS will give light to bud sights 12-18inches deep into the foliage...