um mate have u done any reading on the subject? metal halide bulbs (mh) are use at the vegging stage of your grow, in my own case thats around four weeks, they stop the plant from stretching and allow it to bush up a little before u put your plants into flowering, mh produces light in the blue range of the spectrum which is more like the sort of light the sun gives in springtime early summer. hps produces light in the red spectrum like sun light in mid summer to fall, ur plant will double maybe treble in size when exposed to this bulb. some hpsbulbs are 'dual spectrum' meaning that have a bit of both in them although it tends towards the red, these are what i use and if you can only afford one bulb/light set up its what to go for. theses bulbs produce a lot of heat (mh is the warmest) and u gotta make sure you get rid of that heat with extraction and if ur doin 50(!!!) plants ur gonna need a lot of bulbs, a lot of extraction and a shit load of carbon filters and odor control products or ur gonna smell like an arabs jockstrap. if u wanna grow 50 plants your gonna need a couple of grands worth of equipment. lights, reflectors and ballast,pots, watering cans,hoses, carbon filters,nutrients, soil, coco or hydro gear ....the list goes on buddy, have u never grown before mate? coz if u havent, and it sounds like u havent coz of the questions ur asking, i would suggest your aiming way to high far to fast. 50 plants is a major project even for a very experienced grower and if you dont plan it it right your fucked....
