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Watts per square foot?!?

Discussion in 'Indoor Growing' started by Dually, Oct 20, 2008.


    wattehfck Member

    Is it to much with 400w HPS on a 4.3 square foot area?
    Grow Goddess

    Grow Goddess Well-Known Member

    I have found this to be a very interesting issue. How much light the plants can acutally use, wattage, lumen, square foot, etc. I have been growing in high powered closets for 12 years now. Going by the numbers, it has always worked reasonably for me, until now. Like wattehfck, I have put a 400 W HPS in a space smaller than 4.3 sf. I was running slightly over 100 W/sf. In my new closet, I have encountered something I have not seen yet. I am only running 50 W/sf and it seems far more intense than my old 100 W/sf closet. This has completely baffled me. Lumens and watts per square foot, I no longer consider valuable. It depends on how much light is actually making it to the plants. Then it depends on the reflectiveness, shape of the room, type of light, type of reflector or hood for the light, and so on. It also depends upon if all of the light is coming from one light source or more than one. In my opinion. wattehfck, the answer to your question, is no, I have done it. It worked great. CO2 would be a big help in taking advantage of the 100 W/sf. You better count on a lot of changes with your soil mixtues, size of medium to accommodate the extra light. My opinion about closets with 400 HPS. One 400 Watt is okay for up to 100 W/sf, two 400 W side by side in a closet or closed area, is good up to 65 w/sf. Just my opinion. Something magical happens when you combine two HID lights in an enclosed area. Two 1000 watters in an enclosed area, I definetely do not recommend going over 50 w/sf. Exceeding any of these numbers, CO2 becomes mandatory. When I figured out that watts per square foot and lumen per square foot has been completely debunked, imo, is when I put (2) 1000 Watt HPS in 40 sf closet. That acted far more intense than my 400 W HPS at 100 w/sf. It does not make sense to me, but I am confident. I used a light meter and that is what the light meter tells me. That my 50 w/sf closet is far more powerful. Every grow set up is different, and there are many, many variables. I don't think w/sf or lumen/sf is an all out acceptable way to determine what is enough or too much. A light meter is much more accurate. Here are a couple pictures of my closet that has debunked all my knowledge and experience from the past and all I have read about wattage per square foot and lumen per square foot.
    custom cooled 2000W closet.jpg ----- View attachment 2011342 ----- 012-1.jpg

    I found this post searching for w/sf information. I was looking because I feel that I have exceeded what a plant can use light-wise without utilizing CO2 enrichment. What is confusing to me is that I have done it with only 50 w/sf. I don't feel too confused anymore. I have just accepted that w/sf is a good reference, but not always accurate. Especially when you are using 1000 W HID and combining them in an enclosed area. In my closet, I do not have any problems maintaining adequate temps and my plants are very healthy. I just feel that I have exceeded the useable light for the plants. Next I will be adding CO2 and see what kind of differenc that will make. That will only do me good in the winter though. In the summer it will be difficult because I need to exhaust more heat out. Maybe I will have to add an additional AC so I will not need to exhaust as much air out. I have recently read on other threads that the maximum light is 55 w/sf without CO2 enrichment. Can anyone verify this? In my old growing books, 70's - 80's, they mention 65 w/sf is the max. I suppose with these newer lights it has reduced it down to 55 w/sf. My guess is that the 55 w/sf can also be reduced depending on your equipment, design, etc. I do feel that lumen per square foot may be a bit more accurate, but it is not accurate when it comes to my 2000 W closet. At least going by what my light meter says. I would like to hear more of what others can add to this. I have noticed a benefit going with these high wattage per square foot closets, or grow areas. That even if the plant cannot utilize all of the light, the plant's growth is much different. They do not stretch at all. It doesn't even seem as if they are being grown under HID's . For Example, if I only use one of my lights in my closet, the w/sf stay the same because I am only using half of the closet, then the plants get stretch happy. When I kick on the second light on the other half of the room, the stretching stopped, 100%, but yet the wattage and lumen remain the same. I will look back on this thread, maybe sombody has more information to help us better understand.

    Brandawg92 Active Member

    I know its an old thread but i gotta say i hate when hid lovers dis fluoros. Yea they dont produce as many lumens, but have you ever heard the inverse sq law?? Ive never seen an hps 2" away from a plant. Also its "cleaner" more usable light (in the right kelvin temp). Bottom line same watts, same sq footage, works just as good. Ive tried both.

    And theyre 80% cooler... A/C

    Brandawg92 Active Member

    And grow goddess, yes if youre growing an inch or less a day, you have enough light. Ppl always thinks its great when they do like 6 a day. Smh lol

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