if you grow with metal halide and then hook up an hps light will that start the bud cycle or is changing the light cycle the only thing that can do that
A 12/12 light/dark schedule is what is used to enduce flowering.
Furthurmore, a ballast intended to take MH lamps will not run just any HPS bulb you put into it. You need what is called a conversion bulb and these don't run as efficiently and can cost more then standard bulbs. Switchable ballasts are best as the user can select MH or HPS mode and use the corresponding standard bulb of the proper wattage.
For 12 plants I would use a single 1000w HPS system or two 600w HPS systems to cover all. You can use what you have now, but your results will improve tenfold with higher wattage lights.
