YES they will block the sun light. But you will propably close the windows only when you are listening to music.

Have you ever noticed how much better the music sounds when there is total darkness. I always listen to my acid rock music with all lights turned off - specially my Pink Floyd albums. I read that this is soemething to do with not being able to see the speakers and having the brain place the sound source to the area around the speakers - the sound stage really changes when the eyes dont place the position of the speakers.