I was told that these bulbs would be the absolute best by someone who has done thois before with great results...they are mercury vapor bulbs that produce the right amount of uvb used to properly mimic the sun in a tropical climate, 250-300 microwatts per square centimeter (uW/cm2) of UVB and 2,000uW/cm2 of UVA at a 3 foot distance...most tropical places get about 400 uW/cm2 of uvb at mid day so id say about 2 feet away, use this bulb about 4 hours in mid light cycle for best results, check out the links to read more and tell me what you think, i was looking at the external ballasted zoo one, these also last a hell of alot longer than a normal reptile uvb light that might only last a maximum of 5-`6 months before it looses its power and stops producing uvb light

ReptileUV Mega-Ray Mercury Vapour Lamps for Reptiles - Test Report UV Guide 2006

Mega-Ray® & ReptileUV Products