Thats a good question!!!
This is the first grow I am not. I used to air cool my light. I would have the exhaust fan suck threw the light and expel hot air.
I decided to to take the glass off my light.
I was working on another grow with two lights. One was air cooled with a glass the other was not. I noticed (this could be my imagination) better growth and more trichome development under the light with no glass. So I decided to remove the glass from my hood and see if i can keep the temperature in check without it being air cooled. So far so good. I run my lights from 6 at night to 6 in the morning. I like the drop of temperature the plants get early in the morning when the lights go out. Anyway, the temp has had a max of 83 F. It stays in the 70's when the lights are on and in the high 50's and mostly 60's (sometimes 70's) when lights are off. I live in Northern California.