I always wondered the same thing. In the pic, the light was actually moved up several inches. I kept the total lights about 2 inches from the plant tops.

No heat stress or browning on the very top leaves though, just the oldest first set and now its moving to the other leaves.

I will leave the lights up a bit higher, say 6" from the tops, although I thought CFL should be right next to plants. I can grab light bulb with hands and not get burned...the fan keeps them really cool and my heat removal works almost too well.

Thanks for the input...

Anyother input would be appreciated as well.