Recently my neighbor got a really bright outdoor light on the side of their house and even with black out blinds it wasn't close to enough blockage because light kept leaking through the sides and even pierced the blinds.
The first night I noticed that, I was like "jesus, why is it so bright outside" and I tried to sleep unsuccessfully. I was up until about 3am when I normally goto bed at 11pm'ish. I tried everything to block it on the spot like trying to pile up a sheet near my face but it had no effect since the light just illuminated the room. It was so light that I could see details across the room, like individual fan blades on a 12" fan. I typically can only fall asleep on 1 side but switching sides made no difference either.
So the next afternoon I decided to try an experiment. I took a black garbage bag and completely covered the window. I actually laughed out loud to myself at how dark it was when it was bright outside.
That night was remarkable. I didn't think a room could be so dark. It was the most peaceful sleep ever, except now my TV's little red dot is a distraction where as even pre-outside light it wasn't noticeable.
So if you have trouble sleeping, you may want to try to make your room as dark as possible as a test. Even in hostile lighting conditions a black garbage bag (one of the big ones you would use for leafs) can solve the problem. I hung mine with 2 nails, so when I wake up I just unhook 1 side to get natural light. The only problem is it looks completely stupid from the inside.