Not all Ceramic Metal Halide (CMH) bulbs are created equal. Only the Phillips RetroWhite 250 & 400 watt bulbs are worth messing with. They require a 250 or 400 watt HPS magnetic ballast. The smaller CMH bulbs require a pulse start MH ballast and are not worth the trouble...IMO.

If you have a 250 or 400 watt HPS magnetic ballast?...you can rock & roll with them. I veg with them for 30 days; flower for 4 weeks, switch to HPS for 4 weeks...then, switch back to the CMH for the final weeks to harvest. This seems to expand the buds...and are rock hard.

400 watt CMH/HPS/CMH works well for me...:thumbsup: