One small point about MH lamp bulbs: they can run anywhere from 3000K to 6500K or higher.

HPS lamp bulbs generally are 2100-2700K..unless they have blue added..like Hortilux

I wish peeps talking about MH bulbs would give the Kelvin temp...because of the wide temp range available on the market. I assume; but, don't know?...that the higher MH kelvin temp range (5000-6500k)...puts out more UV rays?

...or the 3000-4500k does?...maryjane; likes the white light..:thumbsup: