The other day I was reading about interior storm windows and happened upon this statistic, screens block 30% of the light coming through a window. So, I decided to test it. I have interior screens on the windows of my sunroom. Here are some compairison shots of the windows with and without screens. It definitely makes a noticable difference.
Now, having the screens on the inside doens’t necessarily let mot heat in in the winter, but it does let more light in which means you can keep your lights off longer. However, if you have screens on the outside of the window that you can remove, you can let in 30% more light and heat into your window. I do have this case on my kitchen windows and will be removing them this fall.