Chop, then fix the eastern tree with the blue beam.
Solve the puzzles by reflecting the beams to the opposite coloured receivers (i.e. blue to yellow, blue+red to green, green+blue to red, all three to black). You'll need to direct all beams to the newest receiver. Due to how mirrors reflect, you often have to reroute, just keep trying different paths for quickest solution. Refer to the full guide if you can't figure it out.
Exit using the ladder in the southeast. (Not the Portal!)
If you die, your grave will appear behind the energised pillar. To get there, teleport to the death altar through the Abyss or the wicked hood if the door to the altar is unlocked. You will have to repeat the energisation process again to re-enter the platform puzzle area. Progress of the light puzzle will also be saved.
Reach the platform with the ballista avoiding the spikes.
The ability to add a choice of destination to your crystal teleport seeds. Talk to Eluned in Isafdar during or after the quest with one fully charged crystal teleport seed in inventory. The teleport can't be added if you are carrying more than one crystal teleport seed. The crystal teleport seed will acquire the ability to teleport to a safe area in front of the Temple of Light, in addition to its original Lletya teleport.