And now I have found more expensive CMHs, with higher lumens and watts. Do these require special fixtures?

http://www.growlightexpress.com/ceramic-metal-halide-bulbs-9/mastercolor-ceramic-metal-halide-400-watt-79.html

It seems like the cheaper CMH would be a great choice for supplemental lighting and that the more expensive, higher output ones would be a pretty cheap alternative to more expensive grow lights. Again, am I missing something?

The 70W bulb you found may screw into a standard medium base socket, but that socket still needs to be wired to a MH ballast. And the 400W bulb requires a 400W HPS ballast as is stated in the description. It also uses a larger mogul socket.

Sorry, but there are no shortcuts to be found here.

indoorgardengal,

That Philips 70w CMH bulb does have a regular-sized medium base, but it must use a high-voltage porcelain(ceramic) socket  not your normal "house lamp" type. You do also have to use a ballast with the bulb. The bulb specifications call for a ballast that meets either ANSI codes M143/E or M98/E. Both of those codes are for low-frequency electronic (not magnetic) ballasts. Some electronic ballasts you will find meet BOTH of those code numbers. Either number will do.

The 400w Philips MasterColor CMS HPS-Retro bulb requires a larger high-voltage ceramic "mogul" socket. It uses an ANSI code S51 ballast. That ballast is normally for a High Pressure Sodium "pulse-start" bulb, which uses an ignitor to initiate the arc. The S51 ballast is magnetic, not electronic, or digital. This is the same ballast used in 400w HPS street lights. I have several of those ballasts which I salvaged from downed lightpoles.

Several years ago, when the Ceramic Metal Halide bulbs came on the market, we speculated in GardenWeb discussions that this might be an excellent bulb for plants. This was evidently a good choice, as growers who tried them have reported "glowing" results. I have yet to buy one myself, even though I do have ballasts for the 400w HPS Retro ones on hand.

Zink