To my knowledge no extensive research has been done to determine the minimum or maximum UVB rays a bearded dragon needs daily inorder to properly synthesize vitamine D3 and thus use calcium injested in food. However, natural unfiltered sunlight does produce much more than any UVB producing bulb available to the public for reptile care. The Mercury vapour bulbs put out much more UVB rays much further than florescent tubes, as much as 10 times the amount.

That being said, I have come across various articles about the importance of UVB rays in the daily lifes of reptiles. Might find them an interesting read. Just want to add one more thing before I put in the links. In the wild, most reptiles are not out and about in the full heat of the day in direct sunlight when the UVB rays are at their highest output. Most reptiles instinctively know when to get out of direct sunlight (either through the heat sensing organ at the top of their heads, or other means) and move to a more shaded area or return to a cooler borrow, crevice etc.

www.hagen.com/usa/birds/info_sheet.cfm?CAT=8&INFO=16

www.reptilerooms.com/Sections+index-req-viewarticle-artid-55.html

www.martinsreptiles.co.uk/ukchams/uvlightingresearch.htm

www.beautifuldragons.com

The last website has a section that shows the various UVB outage at different distances from the basking spot and age of bulb. Thought it would at least be interesting in that aspect. Other websites may turn up by doing a google search on importance of UVB for reptiles or similar search criteria.
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PHLdyPayne

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