As was eluded to earlier, rather than tracing the path of light beams in real-time, today's games typically use lightmaps which are images that change the color of an object making it appear as though a light is shining on it. As with transformations, lighting calculations are done via matrix manipulation, are more complex and are typically computing the distances and directions between light sources and objects. Lighting also takes advantage of the natural abilities of the human eye which are actually more sensitive to changes in brightness than it is to changes in color. To further subdivide lighting in 3D graphics, diffuse and specular lighting are used to simplify modeling the physics of light. Diffused lighting is when light hits an object and scatters in all directions equally and does not depend on the position of the viewer.
Sunlight shining on the ground is an example of diffused lighting.
On the other hand specular lighting depends on the position of the viewer. It also factors in the direction of light and the orientation of the triangle being rendered. Specular lighting can be used to represent the material an object is made from. For example, the difference in lighting a silk shirt versus a cotton shirt.