You gain experience until level 20. If you gain experience after that, you get a Mote of Light (an currency, like gold in other games) that only certain merchants accept. You cannot gain levels using Experience after you hit 20 (you will just keep getting Motes of Light) All armor has stats on it, like intelligence, strength etc. Some armor has another stat called Light. If you equip armor with the Light stat you gain levels past 20. The more Light you have on your armor the higher level you will be past 20. If you take the armor off, you go back down to level 20. You can try to find better armor that has a bigger Light stat, thus increasing your level further. This has NOTHING to do with the Mote of Light currency above. The purpose of gaining levels past 20 is so you can damage higher level enemies in raids and strike missions. Some enemies will be around level 30, so being stuck at 20 will not allow you to damage them. Currently there is no info on what the maximum amount of "Light" armor can have, or what the maximum level past 20 is, although some speculate it to be around 30. In game picture for proof: http://i.imgur.com/xKSrR3k.png