[HeyPK]

I used to use gro-lux tubes with their purple-blue color, and it always seemed to me that the plants were more compact with that lighting than with cool-white, even if i have higher wattages of cool-white.

A high ratio of red light (wave length, 660) to far red light (wave length 730) encourages compact growth.

 

[HeyPK]

Wait! Wait!, you guys!! The studies showed that decreasing the far-red (730) light gave more compact growth. Some of you seem to be looking for bulbs that have higher amounts of far red. If you want compact growth, you want as much red light (660) and as little far red light (730) as possible. When plants are shaded by taller plants, the red light is absorbed or reflected much more than far red. The increased ratio of far red to red causes the internode elongation. Far red reflected off of other plants coming in horizontally seems to be especially effective in causing internodes to elongate.

If we want compact plants, we want as little far red as possible.