On Star Wars the force unleashe how do you end as light side

galen (the apprentice) is told by Vader to create a diversion so the emperor won't notice that he's Vader's apprentice. galen creates the Rebels. the Rebels actually become a serious threat, so Vader made a major screwup. anyways, the rebels are thankful to galen because they don't know he's the apprentice, yeah? so they make galen a sort of hero, and he eventually turns too and then he fights Emperor and Vader (and loses)