Ya I've been wondering about that too, I used 42 watters last grown and got pretty good results. Although i heard 26 watts is more efficient so I'm trying more of those instead this time. The only thing I really like about the 42 watters is they seem to penetrate the plant's leaves more, maybe giving them more energy. Also the range of useful light went further I though, about 4-8 inches being a good distance where 20-26 watters are more effective at about 2-4 inches away. I think the best is people who agree, use a 42 watt on top then use lower watters for side lighting. If you use too many 42 watters you need lots of fan-action because they do get hot, but are still cool compare to my 130 watt CFL with added red. You can see I use, and experiment with all these bulbs I talked about, including repti-glo bulbs. Also I do take light readings with my light meter. Check out my grow
CFL Wrap Around and I would like to continue this discussion as nobody seems to know for sure, just what is better.