UVA and UVB are not the same thing. They are both important to reptile health. UVA is used in a reptile's mental well being and is produced by any "white light" emitting heat lamp and/or from a fluorescent light source. UVB is used in a reptile's metabolism, like in calcium absorption and in food digestion and is only produced in a fluorescent light source, and not just any fluorescent light will do; you need a reptile rated/created UVB light. You will need two separate bulbs, unless you are using a MVB (mercury vapor bulb), to get both heat and both types of UV light. The UVB light needs to be changed every year at the very least to maintain UVB output; after that time, the bulb will no longer produce UVB even if visible light still is.
ZooMed's Reptisun is one of the best long tube style fluorescent UVB bulb, and T-rex makes one of the best MVBs.
Here is a complete website about this:
http://www.uvguide.co.uk/phototherapypho ...
