Yeah, seal the light from thgrow space. There are other threads that discuss the effects of the glass on the light, and it seems to be none or very minimal. Also, i have heard of others having good results controlling heat with the design.

Also, i'm sure you were planning on venting the light space up and out the two holes you will be making on the top of the cab. and maybe using the other 4 on the sides as passive.

That thing looks great. A friend just made one, here, here's the link:

Cabinet