This image does not do anti reflection with 99% transparency justice. But the idea s to clamp down the glass using the aluminium/copper/stainless cover. The cover will continue on the fan side, where it will act fan grill.  

The glass will keep the LED´s dust free and will be easy to clean of. Furthermore, since this concept is aimed at educational purposes,  the glass will also keep curios fingers from poking  possibly hot LED´s.

Two countersunk M4´s should hold the glass firmly in place. 

Since we want the heat to travel through the heatsink and into the cooling air, the isolating layer of air and glass will contribute to this goal. All "used" hot air can be led out if the grow environment. To re-use the heat, there needs to be a devise that can alter the air stream direction, like in a car. This should be relatively straight forward to make using a nema17 or 23. In some cases, like in a Livingroom or  Office space, it may make more sense to went the hot air directly into the space.