They DO block out a lot of light, but they aren't blackout in the sense that the room is DARK.  That being said, I LOVE THEM.  They are heavy but still silky and they can keep out drafts pretty well.  I like that they are washable.   I also love the pattern on this particular pair, which is a departure from my norm.  It's fun.  I would definitely buy these curtains again.  (On a side note, the gray looks more lilac.  Grays are one of those colors that take on different hues depending on lighting and what the wall color is.  If you want a true gray, this is not it.  But they are nice nonetheless and worked for me.)