You can! You need to level up gear that has the Light stat. You just need to find the relevant materials to your gear in Patrol Mode. You can get Ascendant Materials from completing Public Events www.destinypublicevents.com And you can get them from the Daily Heroic strike at higher difficulty levels. You can also get them from breaking down legendary gear. You can purchase legendary gear with Level 2 curible / vanguard / FWC / New Monarchy / Dead Orbit etc Faction rep. My advice, only level up legendary and exotic gear. Its a waste of time and materials to level up rare and below. I hope this helps!