redearslider.com

what is uvb?

UVB is Ultra violet light. A certain wavelenth of light that is in natural sunlight. Your turtle need this light like most reptiles to make vitamin D.
There are two types of UV light A and B. UVA will make the heat you feele when your in the sun. UVB will be the one that gives your sunburn.

Read this sticky about lighting.

http://www.redearslider.com/forum/viewtopic.php?t=10

Does your Setup have UVB light? and basking heat?

UVA aids in psychological well being of reptiles, and UVB aids in healthy shell and bone growth. UVB is necessary

what if you put the turtles in the sun?? well they get the whole package??

The sun is good for them, but unless they're in an outside pond, they probably won't get enough exposure. And if you put them outside, there;s a chance of preditors getting them. I suggest a bulb over the tank. Its easier, they get unlimited exposure, and the bulbs are only 20-25 bucks.

Sunlight is the best source of UVB light;artificial UVB lights give out only a fraction of what the sun does. If you were able to put a turtle out in the sun for a few hours at a time several times a week, his UVB needs would be met. The problem is being able to do it consistently, and in the fall/winter months if it's cool/cold where your are it can't be done at all. A UVB light ensures that a turtle is getting some UVB rays consistently.