CMH bulbs were designed by Phillips to replace the commercial/manufacturing YELLOW HPS lights in their HPS ceiling ballasts; with a bulb that has WHITE light of an MH bulb, without having to change ballasts. They come in two sizes 250 watt and 400 watt, only.

There are smaller CMH bulbs on the market; but they require 'pulse start' MH ballasts.

Digital ballasts are getting better, more reliable. The newest ones; like Quantum have adjustable power settings: 50%-75% and 100%...:thumbsup:

Magnetic ballasts -60Hz
Digital ballasts -up to 240Hz...(they over drive the bulbs, if you get the wrong one)

Again: CMH bulbs require a Magnetic HPS ballast. Either 250/400 watts.