I am bulding a hood/canopy for my tank TOMORROW. It is long over due and I may have missed an important part in my planning...

Here is my question:

How should I vent the hood to release some of the heat from my lights?

I thought about leaving a 1-2 inch gap in the back of the hood below the top opne, but did not know if this is enough...

Please give me your feed back.
Thanks!