There is disagreement about what effect windows have on UV light. However, this is something that can be easily measured with UV meters. The end result is that windows only partially block UVA light, while completely blocking UVB light.
Ordinary window glass passes about 90% of the light above 350 nm, but blocks over 90% of the light below 300 nm.Ultraviolet—Wikipedia
Below 330 nm (UV-B and UV-C), almost 100% is blocked by normal glassUV FAQs—International Ultraviolet Association
Note: If your windows have a special UV coating applied to them, then you should check with the manufacturer to see how it would affect UV light.
The conclusions from this:
- UVA, the type of light known for enhancing bird vision significantly, is only partially blocked by glass. This means that putting a bird in a room with abundant light coming through windows could have a great impact on their lives.
- UVB light is blocked by glass, so there is no Vitamin D benefit from being in a sunlight filled room with closed windows.