[[Caustic (optics)|Caustics]] are a lighting effect of reflected and refracted light moving throughin a medium with curved interfaces or reflected off a curved surface.<ref name=":14">{{Cite web|url=https://developer.nvidia.com/gpugems/GPUGems/gpugems_ch02.html|title=GPU Gems|website=NVIDIA Developer|language=en|access-date=2019-10-30}}</ref> They appear as ribbons of concentrated light and are often seen when looking at bodies of water or glass.<ref name=":15">{{Cite web|url=https://www.dualheights.se/caustics/caustics-water-texturing-using-unity3d.shtml|title=Caustics water texturing using Unity 3D|website=www.dualheights.se|access-date=2019-11-06}}</ref> Caustics can be implemented in 3D graphics by blending a caustic [[Texture mapping|texture map]] with the texture map of the affected objects.<ref name=":15" /> The caustics texture can either be a static image that is animated to mimic the effects of caustics, or a [[Real-time computing|Real-time]] calculation of caustics onto a blank image.<ref name=":15" /> The latter is more complicated and requires backwards [[Ray tracing (graphics)|ray tracing]] to simulate photons moving through the environment of the 3D render.<ref name=":14" /> In a photon mapping illumination model, [[Monte Carlo sampling|Monte Carlo]] sampling is used in conjunction with the ray tracing to compute the intensity of light caused by the caustics.<ref name=":14" />
