HPS is indeed more efficient, however, it emits an obvious red spectrum light, not ideal for foliage growth. Metal Halide is the choice for foliage, with its blue spectrum, where HPS is good for flowering. It all depends what you're growing.

Joe

Joe said it. You need both metal for growth hps for flower so both would be best. The hps is the choice to go with if you only want one.

>> The hps is the choice to go with if you only want one. Not in my experience, unless one is growing a type of herb. Peppers, tomatoes, leafy vegs such as lettuce - they do not need HPS - at all. MH also provides more Mols Per Day, a measurement of the light spectrum plants use to grow.

Mike

Well - I was able to purchase a 400W MH and a 400W HPS. I was lucky enough to get the last HPS lamp the guy had. They are high-bay lights and came with new bulbs and were only $40 each. Couldn't pass that up.