I installed a Fresnel lens on the lower portion of my window door and it worked well. However, small brown spots started to appear on the face of the lens that was against the window some two years after I had put it on. I removed the lens because there were too many brown spots. I tried to clean it but that was impossible.
2006 Dutch Star 4023,
TST TPMS, SMI Stay-IN-Play, Blue Ox Aventa LX,
2011 Toyota 4Runner w Drive Shaft Coupling