If your MH bulb is behind glass, (in an enclosed hood) your ladies are getting virtually none of the UVB. Matter of fact, the glass envelope (the glass part of the bulb) inhibits the UVB before the light exit's the envelope...unless the envelope is cracked, which is a bad thing.

Always use common sense with using UV bulbs. They will cause blindness, and may cause skin conditions if precautions are not taken and adhered to.

Standard and "grow" CFL's and fluoro tubes emit no discernable UVB. UVB bulbs (reptile or tanning lights) emit UVB, and some of the more dangerous UVA.

Instead of worying about specific ratings, a general range is fine. 6000 to 7000 or so for veg, 2500 to 3500 or so for flower. No need to get all anal about specifics here, as different strains will react a tad different under the same spectrums...but not enough to ever worry about. If that worried...go with HID's. (MH or HPS)
Rusty Trichome Reviewed by Rusty Trichome on . mixing spectrums? quick question about CFL lights. I know 6500k for veg 2700k for flower, but I see alot of logs with mixed spectrums. is this better than just switching bulbs? I've got plenty of both spectrums, I just want to know what is best for the plants. Rating: 5