My local lowes has sheets of clear lucite and that's all they have. Can this be used in place of tempered glass? If so how thick should it be?

I doubt they are lucite. The Lowe's here (as well as the Home Depot) sell polycarbonate? If they are, then they will do fine. Keep the UV filter side toward the lamp.

The protective film on them says lucite. I wish they weren't but they are. As for polycarbonate, I asked them and our store don't carry that in stock.

I used lucite as mock lenses and tempered glass when I was building my projector. Lucite becomes a milky white color when it gets warm. And I believe that the maximum operating temperature is 160F.

I stopped off at a plastics house today and ask them about the Lexan. He told me that Lexan is UV safe, meaning that it wont yellow with age in direct sunlight. But does NOT filter out the UV light. He said to get it with a UV filter, it is very expensive and most likely have to order an entire sheet 4'X 8'. They use it in museums to protect artwork or documents.

I just went to our local glass place and bought two pieces of lexan for 5.50 a piece so I'm good to go on that.

I think that like a perforation you're about to be ripped-off. Lexan with a UV filter is sold at my local Home Depot and is certainly not in the least expensive. I have a 18" x 24" piece of Lexan XL-10 that I bought for around $20Cdn. For protection it has a printed sheet attached on one side that explains about the UV factor and that the unprinted side should face the source of the light.