Enough Light?

Hello all,

I am contemplating building a cab that will have approx. 1.75 sq/ft of space in each of two compartments totalling 3sq/ft for the entire cab. One is of course for a veg and the other for a flower. These plants will be raised in soil and either ScrOG'd or LST'd. I am going to use CFL's for both stages on an adjustable height system to keep them as close to the plants as possible. So, if I go with 42watt 2700k CFL's which give off 2800 lumens each in the veg room, how many would I need? I have read that 7k to 10k lumens is ideal, but is this figure the same for both stages of growth? If so, I just want a check here, how many lamps do I need to anticipate buying?

1.75 sq/ft per room at 10k lumens a sq/ft equals 17500 lumens so for this kind of output I would need about [FONT=&quot]6[/FONT] lamps per room totalling 252w per room and just over 500 for the whole cab. In such a small environment, assuming I have a reflector over the lamps and reflective material on the walls, would it be safe to assume I could go down a bit in lumens and save on wattage and space taken up by lamps? Would such a downgrade have a serious and noticeable negative affect on the outcome of my project?

Ideally I have planned this cab for 3 to 4 lamps per room, using these lights I would achieve either 120w and 4800 lumens per sq/ft (with 3 lamps per room) or 1[FONT=&quot]68w and [/FONT][FONT=&quot]6400 lumens per sq/ft (with 4 lamps per room).

So, the recommended amount is 7k to 10k lumens per sq/ft. Under these circumstances and conditions, is skimping going to have a noticeable effect in such small spaces or do I need to redesign and accommodate at least 4 more lamps in total?

~Slomo

/edit: I figure I can tack on another question here too if anyone reads this...to maintain a negative pressure ventilation scheme in my box, hypothetically if I wanted to utilize 3 1inch holes for intake placed in the veg area, how big does my exhausting need to be? If I have it right I think I need to have 2 separate 3 inch holes for exhaust and a fan for each. Will this maintain that negative pressure I want or do I have it backwards?
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Anybody???

It sounds like you have put a lot of thought into it...bear in mind that for vegetative growth,you need the cool white lights...they put out more blue...what about a small hps for your flowering,and use the cfl's for veg...it might actually be cheaper to build,and operating costs(ie,electricity)might be cheaper too...you are the math whiz...lol...you tell me...In my closet grow,I use positive pressure from my intake side to help my exhaust fan vent the hood...my temp runs at 80 degrees when the lights are on

i ran 400 watts enviro in m2 space 80cm head space with a stand free fan wiyh temp no more than 90 on a bad day if that helps in n e way.best of luck.

Thanks for the replies!
I have considered the HPS, at first I even was going to plan the cab around an HPS for the flowering, but of course that leads to the inevitable venting problems that I don't think I can tackle in a space this small. Especially for a first grow, I think I want to keep it to the CFL's for now and keep my inital outlay below $200.

My main question is still, are the numbers I stated in the OP as what my plan is going to be enough or do I need to add more lamps than I had planned for to get into that 7k plus lumen range?

Also, with the negative intake pressure thing, I need to have double the amount of exhaust space as intake to maintain that situation, correct?

~Slomo

yes,you are correct,after a fashion...Ideally,you need to remove more air than can enter,this creates a negative pressure inside...it needs to be well sealed,so that the only air coming in is filtered by your intakes....what I would do is this...a good high volume exhaust fan...go with a larger passive intake...with some sort of closable baffle...this will allow you to regulate the amount of incoming air...this will create the negative pressure you seek.
My question is this,Why negative pressure?....This is My Opinion only,not trying to change your plans......Plants need fresh air,lots of it....So,restricting the intake seems a step in the wrong direction...My approach is this...Give the plants all the air you can...put positive pressure on your cab...hook your light to a passive exhaust and it will vent your hood....push the exhaust with a small fan,or leave it passive,but push it through a scrubber and it will cut the smell....just my opinion of course...any thoughts?

yes,you are correct,after a fashion...Ideally,you need to remove more air than can enter,this creates a negative pressure inside...it needs to be well sealed,so that the only air coming in is filtered by your intakes....what I would do is this...a good high volume exhaust fan...go with a larger passive intake...with some sort of closable baffle...this will allow you to regulate the amount of incoming air...this will create the negative pressure you seek.
My question is this,Why negative pressure?....This is My Opinion only,not trying to change your plans......Plants need fresh air,lots of it....So,restricting the intake seems a step in the wrong direction...My approach is this...Give the plants all the air you can...put positive pressure on your cab...hook your light to a passive exhaust and it will vent your hood....push the exhaust with a small fan,or leave it passive,but push it through a scrubber and it will cut the smell....just my opinion of course...any thoughts?

sorry for the double post...my dang browser is actin' up