in my minecraft worlds go dark and its not night time

in experimental world and normal worlds ive been having alot of problems with my worlds. my worls have been going black with a green light in the middle of the screen. i have to save the game. then i reload it back up and then its ok, but the a few minutes latern it happens again. please get this resolved. im having a hrad time of playing the game because its really making me mad. i love this game. ive been playing this game for 12 years now. thank you.