Well ive been pondering this idea for a few weeks now. I'm not expert but from what I hear LED's tend to produce airy buds. And when running CO2 in a tent you don't want to have any exhaust going? am I correct so far? If so wouldn't running co2 be very efficient with LED's because the don't give off really any heat that would have to be extracted from the tent and the CO2 would help out with the lack of yield while still saving on your electricity bill? I could be way off on this one I am far from an expert on CO2 use so if someone could throw their opinion in on this it would be great
You cant really just seal up the tent... plants need fresh air. You'd have to Flood the sealed tent with C02, wait till the ppm drop below a certain point (with your expensive c02 monitor), then purge the tent, bring in fresh air, the flood the tent with C02, rinse and repeat... C02 systems also need timers (part of that expensive C02 controller you'll need) that regulate the input of C02 to curtian times of the day. without that controll your simply wasting the C02, and wasting any cash; far from saving the few cents thats LED vs HID systems provide (becuase you need to use the exact same wattage of Lighting, your just saving a few Watts of power by not needing as much cooling systems inplace)
I use LED and here's what I've done. In an 8 gallon plastic fermenter I make a sugar wash from 6.5 gallons of water at 80 degrees, 15 pounds of sugar, 1/2 cup bread yeast, 2 tablespoons of epsom salts, the contents of 4 vitamin B capsules, and 1/4 cup of lemon juice. After it's all dissoved well I fit the lid to the bucket. My bucket has a grommet that a 3/8" hose fits in snugly so I run it into a sports drink bottle with some water so I can see the co2 bubble. I drill the cap of the bottle with a 3/8" and a 1/4" hole. I insert the 3/8" line all the way into the water and the 1/4" line just an inch into the bottle. From the local garden shop I picked up a hose punch for making small holes and 1/4" tee. I then punch holes into the 1/4" tubing every 3" I make the hose long enough to encircle the top of the tent and using the tee attached the co2 "ring" I run a solid line it to the bubbler. Now I make co2 like crazy and just vent at regular intervals. It's cheap, effective and if you don't mind something that tastes like Thunderbird wine you get something to drink. Of course with some ingenuity you could distill it and make your own hard lemonade.
Airy buds are not the result of using LEDs, but of insufficent photonic output. Huge difference. You can get airy buds from any light source.
If you're gonna run CO2 I think 1500ppm is ideal, and you don't have to run it in the dark. Also, it'll allow your plants to tolerate higher temps, which means you could probably at that point get away w/ switching up to HIDs, which would give you the density you're looking for w/ out killing the plants w/ heat, because the CO2 would increase their tolerance to higher temps. It might cost you a little more on the power bill, but the increase in weight will probably be more than worth it. There's a guy named rumpleforeskin who's got a few threads on here who's pulled something like 11-13oz off 2 plants w/ a 400w and CO2 in a closet.