Concept:The Sun is a star and the nearest one to the Earth. It produces its own light and heat, and almost all the light energy on Earth comes from it.Solution:The Sun gives out light and heat that reach the Earth directly.The Moon produces no light of its own; it only reflects sunlight.Other stars give light, but they are so far away that very little of it reaches the Earth.Hydro (water power) is a source of electrical energy, not of natural light.So the main source of light energy on Earth is the Sun.Answer:Option C (Sun)