[[File:Ray-traced steel balls.jpg|thumb|Image rendered using ray tracing]]
Light sources emit rays that interact with various surfaces through absorption, reflection, or refraction.<ref name=":72" /> An observer of the scene would see any light source that reaches their eyes; a ray that does not reach the observer goes unnoticed.<ref>{{Cite web|url=https://developer.nvidia.com/rtx/raytracing|title=Introducing the NVIDIA RTX Ray Tracing Platform|date=2018-03-06|website=NVIDIA Developer|language=en|access-date=2019-11-08}}</ref> It is possible to simulate this by having all of the light sources emit rays and then compute how of each of them interact with all of the objects in the scene.<ref name=":17">Reif, J. H. (1994). "[https://users.cs.duke.edu/~reif/paper/tygar/raytracing.pdf Computability and Complexity of Ray Tracing]"(PDF). ''Discrete and Computational Geometry''.</ref> However, this process is inefficient as most of the light rays would not reach the observer and would waste processing time.<ref name=":21">Wallace, John R.; Cohen, Michael F.; Greenberg, Donald P. (1987). "A Two-pass Solution to the Rendering Equation: A Synthesis of Ray Tracing and Radiosity Methods". ''Proceedings of the 14th Annual Conference on Computer Graphics and Interactive Techniques''. SIGGRAPH '87. New York, NY, USA: ACM: 311–320. {{doi|10.1145/37401.37438}}. {{ISBN|9780897912273}}.</ref> Ray tracing solves this problem by reversing the process, instead sending view rays from the observer and calculating how they interact until they reach a light source.<ref name=":17" /> Although this way more effectively uses processing time and produces a light simulation closely imitating natural lighting, ray tracing still has high computation costs due to the high amounts of light that reach viewer's eyes.<ref name=":0">{{Cite journal|last=Greenberg|first=Donald P.|date=1989-04-14|title=Light Reflection Models for Computer Graphics|journal=Science|language=en|volume=244|issue=4901|pages=166–173|doi=10.1126/science.244.4901.166|issn=0036-8075|pmid=17835348}}</ref>
