From the post below about the light tests:
Repti-Sun 5.0 - The Tubes were okay when first on, but dropped dramatically and at 3 months, to the point I do not feel they were very effective at all for bearded dragons, but good for an animal that needs less UVB or is supplemented regularly with Calcium with D3, so we give 'em to the water dragon 
This was at 6 inches, I did not want to put the numbers as we wanted to see what the other person testing found with their test and not taint it.
Our test was mainly to see what degree of constant UVB was hitting the basking areas and cooler areas. Mostly to check the theory that too much UVB was going at the dragons. Even the one with the most output of them all which was the Active UV Heat 100 watt Spotlight @ the recommend minimum distance of 18 inches, it had about 3 times as much UVB DIRECTLY on the basking area with a diameter reading of about 6 inches, and fading to no UVB reading at 12 inches from it. This was equal to Florida sun UVB output in the shade or on an overcast day............. NOT MUCH UVB and we felt certainly not too much UVB.
The floods cast a broader range of UVB output and it extended to still having a decent UVB reading @ 18-24 inches diameter. In a 65 gallon tank, -0- UVB is reaching the far end, so we might as well shut off the UVB when they are on that end brumating, it is not reaching them and they do not need it anyway.
Our conclusion was Mercury Vapor are not too much UVB for reptiles that come from an area that has one of the highest UVB outputs on earth... in fact, even the strongest bulb at the newest point was 4 times less that, in the "HOT" spot. Also we feel since they decrease as you move further away in diameter, they pose no health risk to humans who use them on reptiles as directed.
As for the argument that, "but reptiles are not always in the sun in their native habitat" :
No, they are not, they move to shade or out of the light. In an enclosure, as long as you have 24 inches for them in length to move away, they are not either.
I wish we could have taken all the blubs longer, but the tubes were as low in UVB output at 3-4 months as ESU coil and Solar-Brite 160 watt Globe MV were to start with. I would not keep beardies under them at that point and the other MV lights were fading or going out permanently(except one)..... their UVB output was good...... but they stopped lighting!
It could have been our area and power surges that effected them going out, or they may just not last as they are advertized. We still use PowerSuns and Active UV Heat, we have not had problems having them replaced by the companies, just a lot of shipping back and forth..... I save their shipping boxes now and repack and send them back in it when needed.
One other thing we did learn, no NOT touch the blubs with your hands or fingers, oil on them create a hot spot on the blub and they will affect the functioning of them and use a larger dome, not a small one.