Caustics are formed by light rays that are reflected or refracted by a curved surface or lens. The phenomenon, often visible when light passes through a glass or at the bottom of a pool, exists because of the interaction of uniformly directional light with the fluidly curved surface. In David K. Lynch and William Livingston's book Color and Light in Nature, the surface of water is described as a series of positive and negative lenses. The positive, convex lenses act to concentrated light while the negative, concave lenses direct light away from the interstitial areas, producing a vibrant network of concentrated curves of light.1
Architecture typically plays a passive role with respect to this archetype of light effect. Incidences of caustic effects are often happenstance, and can be dismissed or heralded as serendipitous coincidence. However, it is difficult to deny the curiosity and wonder that is evoked in the viewer when concentrations of light appear in the umbra of the shadow image despite our contradictory common understanding of shadows as being indicative of an absence of or an obstruction of light. The caustic therefore appears as a true secondary layer of information.
Unless viewed in extremely bright ambient conditions, the caustic will always appear to the viewer as superseding the brightness of proximate light effects.
The etymology of the word caustic lies in the Greek words kaiein, 'to burn', and kaustos, 'combustible'. Though caustics require some computational power to replicate, it is possible to digitally reproduce and manipulate their most common forms. This changes the role of architecture from passive recipient to possible instrument with which to tune these fine structures of light.
Though forms can be generated that produce intricate patterns and lines of light, caustic propagation can be resolved in great detail. Research conducted by the Computer Graphics and Geometry Laboratory at the École Polytechnique Fédérale de Lausanne shows that any desired photographic digital image can be reproduced in caustic form when a transparent or highly reflective material is milled with the geometry that computationally corresponds with the image's light and dark areas. Upon exposure to a direct light source, the image is revealed.2 This research, though as of yet tentative in its proposed application, marks the first foray of architecture into the realm of active engagement with caustic phenomena.
1. David K. Lynch and William Livingston, Color and Light in Nature (Cambridge: Cambridge University Press, 2004) 93-94.
2. Thomas Kiser et al., "Architectural Caustics - Controlling Light with Geometry," EPFL Computer Graphics and Geometry Laboratory, accessed April 4, 2017,
http://lgg.epfl.ch/publications/2012/caustics/ArchitecturalCaustics_AAG.pdf.