Extreme lag in min smooth lighting

Extreme lag in smooth lighting-minimum mode.

I'm in a world that has had a huge amount of bugs since I created it, including incorrect entity saving positions (I was on the surface and I was in a cave the next time I logged on) and various other lethal bugs. This world hasbeen created in the first 1.7 snapshots and I have upgraded it to 14w28b over time.

maximum smooth lighting works fine and I am using this resouce pack:http://www.reddit.com/r/Minecraft/comments/2085az/3d_models_resource_pack/(version 2.2.6)

Hope this helps.