Metal halide glass light cover (remove?)

I recently got a 400W metal halide security light Its encased in a brown metal cover which keeps in alot of heat, I was wondering if i should remove the glass cover over the bulb. It keeps in alot of heat, but does it block any light?

Is fixture vented? If not you may want to remove glass so bulb runs cooler. High heat shortens bulb life drastically. If you can leave the glass on the light losses are minor.

No its not vented, and the outside metal does get pretty hott, it was designed to be an outside security light. I think i would rather keep the heat inside the fixture if the bulb life is not affected too much, how much is drastically?

I've never seen figures on this but they replace those bulbs in about 2/3 of the time they get out of open fixtures in industrial apps.

i removed just the glass because on some apps the metal around light is actually made to stay that way lights with internal ballast obviuosly need the metal casing but i have found that my two 400 wts with external ballasts still need the metal casing aswell check it out good before dissasembly cause i made this mistake and spent an hour trying to put all that shit back together again there are wingnuts and lock washers that hold shit together from the inside on alot of lights and it is almost impossible to reasemble these after you take em apart...