To answer a question that Jessi asked on a different forum: it's often reported on the internet that window screens will block out the UVB. I believed it for a long time myself, until a very knowledgeable person told me that it will actually let some of the UVB through. The amount that gets through will depend on the size of the openings and the size of the wire. He also showed us an Australian screen that says it blocks out 30% of the UV, meaning that 70% gets through: http://watsonblinds.com.au/products/crimsafe/

The big problem with ordinary window screens is that cockatiels can easily chew a hole in it. But I made a screen protector out of hardware cloth and wood left over from the aviary building project. The regular window screen is still in the window to keep the bugs out, but the heavier screen in front of it keeps the beaks away.

Here it is with the blinds open so you can see it:


And here it is with the blinds down to keep the cockatiels from going splat against the glass. They do crawl through the blinds to get on the windowsill sometimes, so just having the blinds down is not enough protection for the regular screen.

Oh, I see. That's interesting.

I did try to open the window back when I just had Lucy, though it was more on the intent to see how she would react to wild birds. Of course, the first thing she did was go for the screen, planning to chew it up. I guess I could try opening the window that's next to the table, when the light shines directly on it. Then they could get some vitamin D while on they're sunbathing.

Can the sun shine through regular windows so our birds can get sunlight?

Yes, but windows will keep the UV rays out, so it's really not much better than artificial lights. That's why I was wondering if screens could let UV rays in.

Oh are you sure it keeps every bit of UV rays out im only wondering because I watch the Vampire diaries and if they can burn in the sun from just pulling the curtain thats rays coming in lol but thats not real life.Seriously I can hear a mouse in my parrot drawer it already smells like urine its disgusting I have to throw all the stuff out lucky theres not much toys in there.

Modern window glass (meaning glass that's less than about 50 years old) has generally been treated to help block out UV. Older glass will let more through. But UV rays are easily deflected so some will bounce off no matter what.

Long exposure to UV rays will fade the colors out of carpeting and upholstered furniture, so humans generally prefer not to have unfiltered sunlight beating down through the windows day after day.