There are only three adequate one's most other cheaper one's are inadequate for turtles. The Mega Ray is highly recommended for the best usable UVB ray's and last about 18 month's. I use that one and recommend !!! Yes cost a little more but the other two you would have to buy two or three over time to last as long as the mega ray making it truly cheaper in the long run ! And they produce heat too so only "one" bulb is needed no second bulb for heat as with cfl / UVB's ! Saving more money.
Use the coupon code at this site will make it even cheaper.
http://www.reptileuv.com/about-mac-industries.phpGood video to watch :
https://www.bing.com/videos/search?q=UV ... ORM=VRDGARUVB's are a specialty bulb made of quartz's glass with a special coating to produce the UVB rays. If you have a UVB meter you can read exactly when you need to buy another. If not , in 18 months replace the mega ray. The other two only produce UVB ray's for 5-8 months at best , I tested . Just write down date installed to help. Also for any read the specification on placement ! All speciality UVB bulb's will still produce white light when the UVB rays stop , so a meter helps or use date installed.
Wattage will depend on the size of you setup and what type you have. MVB's are normally meant for large tanks. But Mega Ray last year came out with a 70watt for smaller tanks. 70wattt say for around 50 gallon tanks , 100wt for 90-150 gallon , 160wt used around 200-250 gallon and 275 wt 250 gallon to 350 setup's. These are just my size recommendations based on my use and others I know for wattage.
NOTE: make sure fixture has a porcelain socket MVB's produce both UVB and heat too ! Also check it's rating for the wattage to be used. Most porcelain sockets rating starts at 150 watt and go up from there but check your's .
Very Important when changing a "style" of bulb check the temp's carefully ! MVB's produce heat too ! Best to start at the max distance recommended and adjust down until your temp is reached .