UVB lighting - How much is enough?

[mouser]

....or better yet, how much is too much. I am running a 2x4 with, in an ideal world, 3 flowering plants. I can hang 26w UVB CFLS...or 13w... 1 per plant? 3-4 evenly spaced? can I run them off the same timer or do I want less exposeure? Any help is appretiated!

 

[AKgramma]

50 watts per square foot is the recommended upper limit for an indoor grow. So you are looking 400 Watts (draw from socket, not advertised brightness). I go at least a dozen and sometimes 14 23W CFLs placed above, below, and to the sides, for best penetration. So went with a lower count to keep the heat levels down.

CFL's can come down close and personal to the canopy, just not touching. I grow with mostly CFL's and only recently added some Mars 300 panels to the grow areas.

 

[Lazarus13]

I use one of those uvb cfls per plant and move it around each day to hit different parts of the plant. I set the timer for 2 to 3 hours at a time but have done up to 4 with no ill effects. Since switching to a hid/led combo i dont use them anymore. I swap out my hps for the mh bulb and drop my leds close for the last week or 2 and it does basically the same thing.