Question

Define the art term, light. Describe the purpose and importance of light.

Answer 1

Light is a natural agent that stimulates sight and makes thing visible; illuminate 
the purpose of light is it transfers energy. And the importance of light is a catalyst during photosynthesis in plants. Light is the most important tool of guidance. Light is a means of communication.

Answer 2

Light is the way you see a piece of art. You could see it in a negative or positive light similar to English "Connotations" It's important to see a picture from different light angles because you could see something in one that you didn't in another. 
Hope this helps!