I put a couple of these into use 8 days ago and I've been checking their UVB output nightly with my solarmeter. The first night, after 2 hours of operation, they were putting out over 500 microunits of UVB at a 12 inch distance. They were also providing a basking temp of around 95 degrees at a distance of 14 inches. The UVB output has degraded gradually over the 8 days that they have been in use. Tonight's reading was 259 which is still a good reading. I'm convinced that they are providing adequate levels of UVB for my animals health. I just ordered 4 more and will continue to test their performance.