grow closet question

do i need a peice of glass between my reflector and the tops of the plants. the space is quite confined 2.8 x 2.8 x 5.9, what is the purpose of the glass?? safety feature, thanks in advance

It keeps your plants from growing into the hot light, and i guess it could be a safety issue, also if you have an aircooled hood, it works in confunction with hood to keep air in the hood circulated.
I have an aircooled hood, with the glass lens, and all my plants are 1-5 inches from the hps light. NO BURN.

will it be allright with a 400hps diamond reflector. i have a 295 cfm ruck fan with carbon filter allready, would this be adequete, dont want an air cooled hood because it means purchasing another fan, tight budget, am yet to purchase the reflector, any ideas on what would be good?????