I grow in a shed so recycle heat it’s currently -5c outside and my ladies with no heat except lighting are a nice happy 75f vented hoods are designed to have glass the vent on one side is for intake the other side is for exhaust if you put glass on shade it can pull or push cool air through hood pulling heat away as it goes. In a closed loop fashion straight in straight out I have run 1000w HPS with vent hoods in this fashion at nearly 1’ from my plants with temps in the high 70’s in a 4x4 tent 
radiant heat from the light itself only accounts for small amount of heat compared to open bulbs even with fans pulling some heat away constricted air moves faster and also cools more efficiently. 
those are 2 proper applications of vented shades the only reason to remove glass is to change bulbs done properly the only extra heat will be from shade and ballast
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