When I said it was way off, I mean way too high.. I think the exiting light losses might be much less than 10%..
Here's an URL
Understanding Energy-Efficient Windows - Fine Homebuilding Article
I skimmed it fast, but didn't see any number associated with light going backwards out the window..
Hey, those look like my Low-E windows!!
Just looking at that picture, it seems intuitive that what Sunlight comes in the window, stays inside..
Expect for the regular cold air leaks and low R-factor window leakage..