Originally Posted by chris_zx2

A 13w CFL is equivalent to 60 watts. In terms of cost effectiveness I strongly recommend a minimum of 23w. If you can afford the big ones it would better.
I also suggest half 2700k and half 6500k. Although CFL's are full spectrum you want most of the light to be red and blues. Plants use the red and blues most effectively.
To make it clearer a 5000K bulb may put out 25% blue (6500K) and 10% red (2700K) but the remaining 65% will be in the unusable range. If you use the 6500K and 2700K you will be much more efficient.
Also keep in mind reds (2700K) simulate lower sun for fruiting and blues (6500K) simulate middle of summer for vegetative growth.
As well a distance of 6-8" is ideal for growth.

I know all this is hard to accomplish aesthetically, that is why I build my 10 bulb systems (1000W) in spare rooms and I install track lighting with spot bulbs for public areas.

Here is the color charts showing the spectrum's; keep an eye on the reds and blues:
***sorry couldn't find 5000K but it will be mid range greens to blues.

6500K:


2700k: