ok this may sound crazy but the
metal halide has enough red in it to flower just fine and i have found it can even get bigger results than
hps,in some strains of plants. remember flowering is triggered by daylight hour change not color spectrum. i have been able to grow on a 20 hr cycle and triggered flowering by just reduceing daylight hrs to 14!! ( i do go to 12/12 to make them finish on time) it is a myth that you can only flower on a 12/12 cycle !! how long is mother nature on 12/12? maybe a few days a year, yet flowers seem to bloom outside don't they? i think it is that you need about 30% reduction in daylight hrs or more to trigger flower. blow your friends away, grow faster and with less light equipment, and possibly larger . for more density you can add some supplemental red hps or like me i add t-8 3600k bulb flouresents,low cost.
i have no professional training or skill just a lot of trial and error experiance