You begin earning Mote of Light at Level 20. Each time you would normally gain a level from experience at Level 20, you are instead granted a Mote of Light. They can be used to purchase legendary items such as Warlock Bonds,Hunter Cloaks, and Titan Badges from The Speaker. Mote of light help you level up to the next level beyond level 20.
When you reach level 20 and you earn XP it now creates motes of light. So now how do you increase from Level 20 where it seems that you have reached cap? Well now we get into light and the more light you have the more you can increase your level beyond 20.
1. Check with Warlock Vanguard in the Tower for any light armor
2. Head to Orbit, and choose strike mission “The Vanguard” and complete all the 4 missions that are in it.
3. For more details take a look at the video guide below in which explains how to get more light and armor of light.