Shades/windows that block direct sun but let light in?

[JKeys]

Didn't really know where to put this thread, but....

I'm having a problem with my plants. Whenever it is sunny put, I need to adjust my curtains so that no direct sun hits my plants, Is there a type of curtain that allows lots of light but also blocks out direct sun? (Another reason I am saving for a small greenhouse-I won't have this problem.) I would adjust the curtains, but I am at school all day, and it is the middle of winter, so most of the good light hours are when I am away. Any help would be great. Thanks!