@WhatEvil : Maybe ‘magnify’ was the wrong word choice, but the point is that glass makes it hot inside if you’re trying to keep it air conditioned and don’t have curtains up. Touch a window in the heat of summer and it’s hot, and it’s not because hot air is coming through, it’s because the light is reflecting through. If there are no curtains to block the sun it’s gonna heat up your room.
That’s why they sell stuff like this and or you can do it yourself like this. This explains it better than I.