redearslider.com

"Glass, acrylic, plastic and screens with grids under 1/2" can obstruct nearly all the UVB. "

This makes no sense to me. Can someone explain the science behind this. UVB wavelength is only a couple hundred nanometers. I am curious. I have metal screen blocking my UVB light.

I'm not sure where that came from, but it seems to me to be a bit too general a statement...

I can say that barriers like glass, plexiglass filter out/block most UVB rays from reaching your turtle.

A fine mesh screen will block significant amounts as well.

The screen covers that I've usually seen used on tanks will block about 30% (from what I've read) of the UVB.

Hardware cloth (screen that you can buy in rolls) that has 1/2-inch holes allows much more UVB light to reach your turtle, and this size hole is often suggested as not being an issue with regard to UVB light (but some will still be reflected/filtered out) particularly with set-ups that are outdoors and need protective covers (although the larger holes would make them good for indoor use as well.

You say you have a metal sceen between the UVB light and your turtle. How big are the holes in the screen? What UVB light are you using? Are the UVB light and fixture being placed on the screen above your turtle? How far away from the light is your basking turtle?

It's a general statement from the main pages on the site. Screens are said to block 30-60%, depending on the type of screen, the source and UVB strength (It also depends on what many manufacturers might say or claim) and I'll rather group the smaller grid screens as obstructions. It's also a way to suggest to people that they shouldn't keep their tanks near windows, which is something that needs to be reminded of often.

I'd much rather be extra cautious and you'd find references for larger screens on many sites that pre-date this one. I would like more accurate readings of UVB but have only come across one or two sites that collect this type of data. However, how they conduct their testing may not necessarily reflect the conditions that basic keepers will be using artificial UVB. Well, anyway, that's my reasoning for a statement like that.

The above statement sent me on a google search for about an hour last night. I found dozens and dozens of sites that talked about glass & plastic blocking nearly all (95%) of UVB rays, but not one about screens. Although it just makes sense to me that the smaller the holes are the more rays would likely be blocked. I agree with Steve, I'd rather be cautious and not harm my turtle.