Originally Posted by
raybark
In order for a plant to grow and bloom, it must (among other things, of course) absorb a certain "volume" of photons. What that light source is appears to be less of a factor than the sheer number of photons they put out.
Your HID lamp puts out a ton of photons, but mostly in the blue end of the spectrum. Folks also successfully grow under HPS, which is mostly in the red end. When I started, I used 50/50 wattage-wise incandescent bulbs (red) and cold white fluorescent shop lights (blue). In LEDs, you can go with red and blue, or white, and as I have been saying over and over, as long as the photon flux and the duration of exposure are sufficient, you're golden.