Is lexan bowing the fresnel only due to improper mounting/cooling or is it due to heat? If I glue my fresnel to the lexan using silicone I (not II) do I need to put a bead (sp? I mean line) all around the fresnel?

If I can't prevent bowing I'm thinking of seperating my fresnel from my heat shield, but then how do I cool the gap?

I'm using a technique close to your second diagram. I've already got enough twists and turns in my air path, I'd like to keep it as straightforward as possible to minimise disruption and maximise airflow. Also, having the air exit out the bottom into the light chamber lets convection help with air flow. That's a relatively minor help, but any help which comes without a noise penalty is welcome, IMO.

well.....you would be hard pressed to *melt* the lexan without having serious problems elsewhere so your bowing is most likely related to too tight of a fit. It should be able to freely move around in its mount so that when it expands (it will) it will do so evenly in all directions (theoreticallly).....i have my lexan about 2 inches from one of the BIG bulbs...then about 3-4 inches to my fresnel and have experienced no problems for a few weeks now....anyway.....the lexan should be sacrificial.....if you have to replace a 12 dollar sheet every 3 months....(you wont)..who cares?