CheriS has a UVB meter and has done some testing of her own. She has done testing on many commercially available lights and still highly recommends replacing the tubes once every 6 months, minimum.
A light that was discovered even better than the ReptiSun 5.0 is the Exo-Terra 8.0. It had good output past the 6 month mark, while the ReptiSuns were beginning to diminish.
Here's a link to the article about her findings. Remember, she has no vested interest in any of these companies, her one and only concern is what is best for the lizards.
www.reptilerooms.com/Sections+index-req-viewarticle-artid-14-page-1.html
If you replace your tube bulb every 6 months, and keep it within a reasonable distance (I'd say no more than 8 inches) you can be sure you're providing at least adequate UVB for your lizard. If you don't have a UVB meter to test it yourself, then simply get it closer to the basking spot and replace the bulb every 6 months like clockwork.
We've learned through many bad products on the market that you unfortunately cannot always trust the manufacturer. Better safe than sorry.
Of course, none of that applies to MVBs, they are in a whole other league.
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Amanda
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2.0 bearded dragons (Ocho / Domo-kun)
1.0 pictus gecko (Nicodemus)
0.1 kingsnake (Rio)
0.0.1 tarantula (Calcifer)
1.0 ferret (Playstation)
1.0 cat (Wally)
0.1 dog (Tima)