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I just read on another site that when you have a screen cover on the tank, it prevents the uvb from reaching the basking spot. Is this true? I use a Reptisun 5.0 tube and it rests on one of those mesh screen covers you get from the pet store. My RES likes to try to climb out of the tank so I need it covered. The light is 6" away from his basking spot. Should I get a 10.0 to increase the amount of UVB that goes through the screen or is this not much of a problem at all?

A mesh screen will reduce the amount of UV light reaching the animal. A fine mesh screen will filter out more UV than a screen with wider openings. If the bulb is only 6" away then the turtle is still getting some UV. If you can supplement that with some outdoor sunlight a few times a week, you should be all set. Otherwise, you could try getting a 10.0 bulb (maybe wait until the current bulb is past 6 months old), but keep an a close watch for eye irritation if you do. For what it's worth, I use the 5.0 tube lights over my baby lizard grow out tanks through screen mesh with no problems. but I also supplement their diet with vitamin D3 (which the UVB helps them produce naturally). Between the two sources my lizards all grow to healthy adults with no calcium deficiencies of any kind.

I've read that the standard screen covers for tanks will screen out about 30% of the UVB rays that would normally reach the basking turtle without it. The light's distance from the turtle will also affect how much UVB the turtle gets.

Ok, thanks a lot! The cover I have is fine mesh so I will go out and try to find a cover with bigger openings. That should help some for now.

Here's a 1/2" screen cover I made:
http://www.redearslider.com/forum/viewt ... c&start=45

Scroll down about halfway.....
It's pretty easy to make if your handy. I got everything at Home Depot.
If your are going to place the light fixture directly on the screen, don't get the screen with vinyl coating, it may burn.....just get the plain metal type.

Wow, grey goose, that was very helpful! Thanks so much for the idea!