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The big problem with the glass cover is the dust, mine was always dirty and reduced lumens. Some type of dust filter on the air-in duct would help.
I got a light mover and ditched the cover. Your fan and ducting attached to your air cooled hood will draw air up over the bulb if you have no cover, works well to cool things (not as good as a glass cover obviously). I've run mine with a light mover and without the glass cover, air out through ceiling, and it works great. 600W @ 12"-14" from tops and no heat stress.
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