Carol, I can't answer your question since I am growing tropical plants, mostly orchids, under those lights. My lights are timed to come on at 3:00 PM and go off at 9:00 PM. I am simply supplying more light because the sun is so low in the sky during the late fall and winter months. All my tubes are 5000-6500K, and the new T5H tubes are all 6500K.
Do put your hand close to the tubes after its been on a couple of minutes and see how much heat there is. That's the key element here. My T5H tubes really get hot, similar to an incandescent bulb, but my T8 tubes stay cool. You want your plants as close to the light source as possible but not so close that the leaves would burn. I can put plants' leaves within 2" of the T8 tubes but no closer than 12" to the T5H tubes. There is that much heat difference.
