Editing Ray tracing (graphics) (section)

===What happens in nature (simplified)===
{{see also|Electromagnetism|Quantum electrodynamics}}
In nature, a light source emits a ray of light which travels, eventually, to a surface that interrupts its progress. One can think of this "ray" as a stream of [[photon]]s traveling along the same path. In a perfect vacuum this ray will be a straight line (ignoring [[general relativity|relativistic effects]]). Any combination of four things might happen with this light ray: [[Absorption (electromagnetic radiation)|absorption]], [[Reflection (physics)|reflection]], [[refraction]] and [[fluorescence]]. A surface may absorb part of the light ray, resulting in a loss of intensity of the reflected and/or refracted light. It might also reflect all or part of the light ray, in one or more directions. If the surface has any [[Transparency (optics)|transparent]] or [[Transparency (optics)|translucent]] properties, it refracts a portion of the light beam into itself in a different direction while absorbing some (or all) of the [[Visible spectrum|spectrum]] (and possibly altering the color). Less commonly, a surface may absorb some portion of the light and fluorescently re-emit the light at a longer wavelength color in a random direction, though this is rare enough that it can be discounted from most rendering applications. Between absorption, reflection, refraction and fluorescence, 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, reflective and fluorescent properties again affect the progress of 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.