I assume you have a UVB bulb already? Not sure if normal bulbs give off UVA or not. I know they don't give UVB though. Plus, I think most UVB bulbs give some UVA, and UVA is more related to appearance (I'm guessing quite a bit because I am not 100% sure)? Either way, UVB is more important. Go ahead and invest in a mercury vapor. Heat UVA UVB at a lower yearly cost:
2 years incandescent UV tubes = $10x8(1 every 3 months) $25x4(tubes need replacing every 6 months)=$180
2 years mercury vapor=$50
The MVB's are warantied 2 yrs at 12 hrs use per day. Give or take a few bucks on the incandescent UV tubes combo depending on size/wattage and how long the heat bulbs last for you. Either way, I love MVB's and you can see a little investment saves a bit.
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-Bill
1.0.0 Albino California Kingsnake
0.1.0 Colombian Red Tail Boa
1.0.0 Jackson's Chameleon
0.0.1 Bearded Dragon
0.0.1 Argentine Black and White Tegu
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