When you purchase fluorescent tubes, you'll see them called "cool-white", "warm-white", "full-spectrum", etc. All those names related to the Kelvin, which is the wave-length of the light emitted. Warm-white is something in the range of 3200-4500K (it looks pink/yellow), cool-white around 5000K (yellow-white), and full is around 6500K. The 6500K is good for growing (green growth) and the "warmer" ranges induce flowering. In my six-tube fixtures I use 4 tubes of 6500K and two of 4000K. That doesn't mean that what I do is ideal or even correct. Its just what I do.
I hope this helps some.
