Defenestration? ;-) I can see how the contrast issue could be difficult for him if it is right against a window. Possibly some blinds or barrier that only surround his the screen so that light isn't hitting his peripheral vision so hard? Other than that I could only suggest re-orientating the desk but I suspect you've already thought of that!

I have had some success in the past with the suggestion Jodie made. We had vertical binds with quite wide slats and if angled at 45 degrees the user can not see out, but natural light comes in. Now light will still bounce off the blind, so it will still have a brightness, but may be acceptable. I assume the objection by the others is light levels as they should be working, not looking out the window :0) Chris