What is a light bender?

Answer 1

Correction there are no official light benders. Ang is the first human light bender. Before the avatar beasts such as the lion turtle he road in the last few episodes were light benders. Images of the lion turtles were seen in the library episode. Also its not called light bending its energy bending.

The Lion Turtle answered, "The true mind can weather all the lies and illusions without being lost. The true heart can touch the poison of hatred without being harmed. Since beginning-less time, darkness thrives in the void, but always yields to purifying light". The Lion-Turtle brought up a paw, his two claws touching Aang's chest and forehead, causing a green light to illuminate. It is likely that the Lion Turtle used Energybending himself to impart the knowledge of the art to Aang.

ref:http://avatar.wikia.com/wiki/Energybending