This is very interesting. People are using all of the lights on this board but I have yet to see some kind of scientific comparison test. Instead we see success or mixed success with each and every light. It doesn't look like there will be too many objective side by sides. No clear winner either as far as I can tell. In my limited experience I know that HIDs work well for veg and flower indoors. CMH or LED I'm reserving final judgment, most of the evidence for the public might be on these forums.
WELL, my first grow op with the CMH is gone and I'm enjoying the buds.
The man difference, with a 400w hps, is the UVB and the effects on plants are quite clear: more resin, more trichomes, much more flavour and potency.
I think it's more than enough for a "grow you own" grower like me.
Can't say enough about quantity because I did a very short veg period on only 4 plants.