How much light for how much square footage?? Newbie question

Hey Buds & Budettes...
I'm building a 4x4x8 foot free standing growbox and already have bought three sheets of 4x4x8 luan a couple of sheets of 3/8th and an armful of studs and strapping so I am ready to go. I'm thinking single crop at a time growing and don't plan on cloning or overlapping grows.
My only problem is LIGHT!! Not concerned with growing them out under Four foot fluorescents or a bucket load of CFL's. I just can't seem to find a formula to advise on how much and what is the best light to go with for flowering.
The box will be on it's side (right?) and that seem to make sense and the home I have for the box demands it anyway. Will two 400 watt hps light be enough or do I have to go More?? Will my regular fluorescents and CFL's work in conjunction with halide and sodium?? Price is important but not overly critical. I figure I could even finish under old fashioned fluorescents but don't want to waste my time or the cost of seeds trying.

PS!!!! I would even read a book if someone can recommend one not brimming with product prostitution. Thanks guys and gals..

For a 4x4 area a 400w or 600w is perfect (as long as u can keep the temps down). My general rule is 100w per plant / 50 watts per sq ft. I would recommend you run one or two 400w (technically 330) phillips Ceramic Metal Halides (mh & hps bulb in one). They can be used for both flower and veg. Burns much cooler then reg phs or mh bulb (dropped my temp down by 5+ compared to reg MH bulb) and save u electricity. Google advanced tech lighting cmh and watch the videos. Great info.

I have one these in my 4x2 and am very happy with it. Temps stay below 80 even on the hottest days here in socal with no AC, only 4in exhaust fan.

Links in my signature if u wanna check out my grow.

Rottedroots said:

Hey Buds & Budettes...
I'm building a 4x4x8 foot free standing growbox and already have bought three sheets of 4x4x8 luan a couple of sheets of 3/8th and an armful of studs and strapping so I am ready to go. I'm thinking single crop at a time growing and don't plan on cloning or overlapping grows.
My only problem is LIGHT!! Not concerned with growing them out under Four foot fluorescents or a bucket load of CFL's. I just can't seem to find a formula to advise on how much and what is the best light to go with for flowering.
The box will be on it's side (right?) and that seem to make sense and the home I have for the box demands it anyway. Will two 400 watt hps light be enough or do I have to go More?? Will my regular fluorescents and CFL's work in conjunction with halide and sodium?? Price is important but not overly critical. I figure I could even finish under old fashioned fluorescents but don't want to waste my time or the cost of seeds trying.

PS!!!! I would even read a book if someone can recommend one not brimming with product prostitution. Thanks guys and gals..

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A 600 watt hps would cover a 4x4 area nicely and will produce good growth, two 400 watt lights would be even better in my opinion as long as you are not growing anything over 3 of 4 foot tall plants. If you can cool it a 1000 watt would be the best, and would produce explosive growth, but would be hard to cool in that amount of space. Any of those would light combinations would make for a nice grow space that will turn out some good results as far as light is concerned. Also don't forget to put reflective material on the walls or paint them flat white so you get all the light you can to your plants. I hope this answered your question or at least helped you out a little. Good luck with your grow.

robert 14617 said:

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Those charts do not apply to growing cannabis, that would be an extreemly underlit grow space that would produce very little bud for the given area.

Yeah ur right bout that. If u got a 400w in a 5x5 that's 16w per plant, definetly not enought light.

Thanks... Lots of good advise!! Hey Nug what are the demensions of the light in your link. Not concerned with length and width but what cha got for height?? Will I be able to grow effectively if the max operating height I have is four feet? I might be able to go 5x6) but was hoping to get every inch out of a sheet of plywood.

It sounds like you guys think 400W would be good but that 600W would be better if I can keep the box cool. I don't think that will be a problem as I can vent directly outdoors and here comes a New England winter. I think I will go with two 400's but gotta look into the Phillips on your link bud.

Vette I gotta couple gallons of Kilz around. Will that give me the same reflective value as a flat latex paint?? Is Milar(sp) worth the cost or will the Kilz do the trick. I also have a lot of access to commercial duct wrap. Don't know what if anything I can do with that.

Is an eight foot ceiling a big improvement over a four or do you just veg and flower for less time. The chop saw is warmed up and ready to go but the measure twice/cut once theory is in full effect

I assume roberts light spec would work fine Vette but that the plant can handle and thrive on more??

Last thing for now.. Can you have to much light as long as your plants are not getting cooked by the heat?

Rottedroots said:

Thanks... Lots of good advise!! Hey Nug what are the demensions of the light in your link. Not concerned with length and width but what cha got for height?? Will I be able to grow effectively if the max operating height I have is four feet? I might be able to go 5x6) but was hoping to get every inch out of a sheet of plywood.

It sounds like you guys think 400W would be good but that 600W would be better if I can keep the box cool. I don't think that will be a problem as I can vent directly outdoors and here comes a New England winter. I think I will go with two 400's but gotta look into the Phillips on your link bud.

Vette I gotta couple gallons of Kilz around. Will that give me the same reflective value as a flat latex paint?? Is Milar(sp) worth the cost or will the Kilz do the trick. I also have a lot of access to commercial duct wrap. Don't know what if anything I can do with that.

Is an eight foot ceiling a big improvement over a four or do you just veg and flower for less time. The chop saw is warmed up and ready to go but the measure twice/cut once theory is in full effect

I assume roberts light spec would work fine Vette but that the plant can handle and thrive on more??

Last thing for now.. Can you have to much light as long as your plants are not getting cooked by the heat?

Click to expand...

When you say killz I assume you are reffering to their flat white latex primer and if so that would work just fine, but remember to give it plenty of time to set and harden so that it has fully quit producing toxic vapors that may hurt your plants. It can take anywhere from 2 days to a week depending upon conditions (tempurature, airflow, ect). And yes milar would be better but only by a very minimal amount in my opinion, so if you already have the killz thats what i would use. An eight foot ceiling would be better as it would be easier to cool and it would give you the ability to grow larger-taller plants, but then the penetration of a 400 watt light would not be suffecient for that kind of grow. And finally as far as "too much light" there is no such thing as long as you can controll the heat and bleaching dosen't become an issue. If you have everything else dialed in (ph, soil, ferts, temperature, ect.) then in my experience the more light you have the more your plants will produce period. I hope you find some of this information useful. The single best piece of advise that I can give you is keep reading and learning. Knowledge is the single biggest improvment to any grow. I have been growing a little over 2 years now indoors and I have just this week completed my 21st year outdoors, and I still learn somthing new almost every day. Good luck and happy growing.