 Without lighting models, replicating lighting effects as they occur in the natural world would require more processing power than is practical for computer graphics.This lighting, or illumination model's purpose is to compute the color of every pixel or the amount of light reflected for different surfaces in the scene.There are two main illumination models, object oriented lighting and global illumination.They differ in that object oriented lighting considers each object individually, whereas global illumination maps how light interacts between objects.