1. Get a solar sword from Shaxx. 2. Infuse above 280 I believe. (Shouldn't be difficult now that light is 400 max.) 3. Fill all the upgrade bubbles. A new one appears after you infuse above target light so don't forget that one. 4. Speak to Shaxx for the questline. Note: I'm pretty sure you need to finish the Taken King story missions first and some quest to be able to get the solar sword from him. Not sure if that changed now that he sells them. Note 2: after you get your first sword the second and third swords do not require a large part of the grind quest. No crucible kills necessary for example.