Thanks for the info! One of the things I was wonder is if there is a problem with air blowing on or near the bulb and I finally found an answer to that from a Reefkeeping article:

"Hello Lights, a popular aquarium lighting company, kindly assisted me and researched the issue of air flow on and around the bulb in the IES Reference Manual. The manual stated, "With HID equipment [such as metal halide], temperature variations have practically no effect on light output." In order to affect the light output the arc tube's temperature would have to be changed, and since the arc tube is running at such high temperatures, any ambient temperature variations are negligible. The bottom line: unless you are blowing a huge fan right on the metal halide bulb, you will not affect its function or damage."