I have the fastest computer in the house(not a monster gaming machine but still quite nice) and it can hardly run smooth lighting at all. When i do enable smooth lighting with all setting turned down i still get the sames frames as with all settings turned up and smooth lighting yet when i turn smooth lighting off and all setting up i get 80+ frames. I have an AMD A8 4500m APU and it runs slower then another computer we have in the house that has intel graphics that it usually runs much faster than. I should also probably mention(do to the fact this might help diagnose the problem) that when i enable smooth lighting little blue dots appear on the faces of all the blocks. I have not had this problem before the 1.5 release