What Causes To See Dark Shadow In Dim Lights And Dark Places?

Hello. I was playing soccer today and got hit with the ball right on my left eye. I only felt the pain for that second and it disappeared. But, when i was in bed trying to sleep, i noticed a dark shadow under my vision of the left eye. When i closed my right eye(which is fine), i could only see half of my lamp stand, mind you, this is all in the dark. I freaked out and turned on the light thinking i was going blind. But, when i turned on the light, my left eye(the problem eye) would see just fine and i didnt see that dark shadow. I only see the dark shadow in dim lights and dark places but when i go into the light, everything is just fine. Anyone know whats wrong?

I am 16, 140lbs, 6 feet and no medical history that seems important.