I don't think I can fix it the right way because things are missing.
Sprites are not currently sent normals? I tried to add the normal values to the shader program anyway but it's not working.
Until this is fixed you can't rotate sprites nor flip them otherwise it breaks the lights. You'll have to make animations for each direction with their own normal texture pairs.
There is probably still a workaround related to sending more information to the shader from the object being lit but that's kind of lame because it can require a script for every single thing being lit or a manager which knows about everything.