To get this achievement you need to train all of the Light Side force powers. There are 21 in total:
Heal -> Improved Heal -> Master Heal
Force Aura -> Force Shield -> Force Armor
Force Valor -> Knight Valor -> Master Valor
Force Barrier -> Improved Force Barrier -> Master Force Barrier
Revitalize -> Improved Revitalize -> Master Revitalize
Stun -> Stasis -> Stasis Field
Stun Droid -> Disable Droid -> Destroy Droid
Edit: It seems you also need the Force Enlightenment power that you only get after finding all the Jedi masters and going to Dantooine as a light side character. As soon as you get this it should unlock.
Since Master Revitalize requires level 21 to train, training exclusively Light Side powers, you should be able to obtain this at level 21 for a Jedi Consular or level 22 for the other classes edit: though you will need to get to the third act of the game to for the last power so you will likely be much higher in level.