Heat is generally caused by production of light. And production of light (which is measured in lumens) and watts (which are a measure of power) aren't really related. So wattage doesn't directly affect heat...think of it like this. A 150 watt incandescent bulb uses the same amount of power as a 150 watt HPS bulb. But the HPS bulb is much hotter. That's because it's energy usage is more efficient; it's creating a lot more lumens than an incandescent bulb of similar wattage. Direct light is what causes heat. We think of air as solid, but it's composed of millions of molecules. When light waves (energy) strike these molecules, the molecules move more quickly, and the air gets warmer. More light = more energy = more movement = more heat. When light energy strikes plants, the plants absorb it and convert the light energy to heat and chemical energy for photosynthesis.

CFL's have a larger surface area for heat dissipation, so you're pretty much on about the light coming from a single point creating more heat. And most CFL's are slightly less efficient at converting energy to lumens than HPS bulbs. A 150 watt HPS bulb will produce about 15,000 lumens; a 23 watt CFL produces about 1650. 6.5 of those 23 watt bulbs would take 150 watts of energy, but only produce about 10,750 lumens. So HPS is hotter because it has less area for heat dissipation and is more efficient at producing lumens. Got it?

You really need at least 2500 lumens a sq. ft. to grow decently; over 4000 is a lot better. A 150w HPS, like I said, will produce about 15,000 lumens. You could get a marginal 6 sq. ft. grow with it, or a pretty good 4 sq. ft. grow with it. 200w of CFLs will probably give you about the same amount of lumens. The CFLs will be cooler so you will have less problem with heat; they are less efficient, so you won't get the light depth into your plant.

That's enough math and science for now. It's just my opinion, but a lot of bad grows have to do with wasted light. CFLs with reflectors shine light in all sorts of places where you don't necessarily want it. IMO, a good CFL grow with reflectors isn't much worse than an HPS grow, although it will take more CFL watts to produce the same amount of energy. You're going to get bigger yields with HPS...maybe 25-50% more than a well done CFL grow; more than twice as much as a grow done with lousy CFL placings and no reflectors. But you also have more issues with heat, strewss, and ventilation...and in a small areas, that can be a deal breaker. So it's up to you, man.
Roughrider Reviewed by Roughrider on . 200w CFL vs 150w HPS So I have 200w of CFL lighting going on 4 plants to cover approx. 3 square feet. Question: Would my yield increase if I used a 150w HPS instead to flower? Also, if I went up to a 250w hps would that double my yield for just another 100 watts? Say 6 square feet instead of 3. And how much power do all these different lights actually pull when you include the ballast? Rating: 5