Levels and light have been redesigned in Destiny: The Taken King. Most stuff isn’t gated behind your character’s level now, but the Light level instead….

When you hit Destiny’s base level cap (20), higher level gear items get additional stat named Light. This stat is very important in your further leveling, because you stop gaining levels from experience points, but based on a number of Light points on your gear.

What to do next in Destiny when you hit level 20? Focus on collecting new PvP or PvE gear through the end-game content that awaits you.