I use a self stick diffuser material & have been for the past 4 years. When I set up my first full spectrum diy light, I tried lenses, no lenses & still had color banding or "spots" on my rocks/sand, mostly from the OCW red & cyan. I did some digging & found a guy on RC that tried some different ones with a par meter on a dry & wet tank. The best one that he found was a self stick diffuser called "sand" from an online company called BerlinWallpaper (now out of business). The results of his tests were a 5-7% loss of PAR, reasonable to me at the time for eliminating the color banding. I ordered a roll for $10, which thankfully will last me forever. I installed on my acrylic splash shield & couldn't believe the difference! No more spots on my rocks/sand and plenty of shimmer. I just built a new light with pucks for my new tank & also put some on the splash shield, great shimmer & no color separation. Love it & wouldn't have a light without. I'm also a believer in no lenses for better color mixing, but the diffuser definately helps. Mine sits about a 1/4" below the diodes & the light is mounted 10" above the tank. There's some credibility to this claim, especially with the right material!