Well one more piece of advice before I hit the sack, this is to help quality and it will take away from yeild a little since the plant uses more energy creating tricombs & resin.
I ran across this info while doing research in the "advanced" threads. I first read a paper done by a student at Columbia (I think). It was a scientific study about why the same strain of marijuana will vary in potency when grown outdoors at different altitudes. The answer was UVA & UVB exposure. UVB is the main factor and the UVA is more of a multiplyer. It helps the UVB be more effective. I couldn't find any info on UVC, but I can't find a bulb with a UVC rating anyway so I guess it don't matter.
The UVB causes the plant to protect itself by making sunscreen, and sunscreen to a plant is tricombs & resin. This is the only light spectrum that your plants would be getting outside but aren't getting from the CFLs. (MHs have a very small ammount of UVB, but not enough)
If you want to try this you can get a 10.0 UVB Reptile bulb from your local Petsmart for around $30 and you can get an 18" light fixture to fit it for $7 at Wal-Mart. These bulbs have 8% UVB & 23% UVA. They're the best ones that are currently available.
Warning: You have to be extra carefull with this bulb. The higher level of UVA can burn your plant, so don't use a mylar reflector and start it 3' or 4' away at first. Check on it every half hour and move it closer to the plant slowly. Once you see the tips of the leaves getting brown that's when you know you're a little too close, just back it off to where it was before you moved it that close and your golden.
I haven't used this yet but I will as soon as flower starts. I did a bunch of research on this and I'm convinced that it will give me the best buds in the area.