Page "Ray casting" Paragraph 9

In nature, a light source emits a ray of light that travels, eventually, to a surface that interrupts its progress.

One can think of this " ray " as a stream of photons travelling along the same path.

At this point, any combination of three things might happen with this light ray: absorption, reflection, and refraction.

The surface may reflect all or part of the light ray, in one or more directions.

It might also absorb part of the light ray, resulting in a loss of intensity of the reflected and / or refracted light.

If the surface has any transparent or translucent properties, it refracts a portion of the light beam into itself in a different direction while absorbing some ( or all ) of the spectrum ( and possibly altering the color ).

Between absorption, reflection, and refraction, all of the incoming light must be accounted for, and no more.

A surface cannot, for instance, reflect 66 % of an incoming light ray, and refract 50 %, since the two would add up to be 116 %.

From here, the reflected and / or refracted rays may strike other surfaces, where their absorptive, refractive, and reflective properties are again calculated based on the incoming rays.

Some of these rays travel in such a way that they hit our eye, causing us to see the scene and so contribute to the final rendered image.

Attempting to simulate this real-world process of tracing light rays using a computer can be considered extremely wasteful, as only a minuscule fraction of the rays in a scene would actually reach the eye.