5 points
I have internal curtains and blinds and this actually still works well, at least better than keeping them open. Maybe it would work better with externals but this is still worth doing if all you have is internal
1 point
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2 points
Well, the more light you reflect out the better (I would expect that, for example, darker color curtains would be a problem) and ideally you want that whatever light does get converted into heat does so outside.
As it so happens, were I live the heat has been a problem in the Summer since well before AC was invented, so roll-up external shades are standard for all houses and apartments and that stuff definitely works if used as I described it.
