Energy is the ability to do work. There are different forms of energy and they can be converted from one form to the other.
Heat energy is due to the changes in temperature of a body. When a body is heated, the electrons excite and gives off radiant energy which are visible to human eye. We often see red light when a body is heated.
Solar energy can be absorbed by organisms to produce light. Such an example is bioluminescence in some organisms. During the day, they trap solar energy that they glow with at night.
Electrical energy can also be used to produce light. We often see this in lightning and electrical bulbs in a circuit.
