In optics, a caustic is the envelope of light rays reflected or refracted by a curved surface or object, or the projection of that envelope of rays on another surface. The caustic is a curve or surface to which each of the light rays is tangent, defining a boundary of an envelope of rays as a curve of concentrated light.
A piece of milled plexiglass acting as a projecting lens; via the Computer Graphics and Geometry Lab at the École Polytechnique Fédérale de Lausanne
New milling techniques applied to glass and plexiglass panels could be used to “create windows that are also cryptic projectors, summoning ghostly images from sunlight.”
[Pauly and Bompas] hope that the technique will be used in architectural design, to create windows that mould sunlight and throw images or patterns onto walls or floors,” which, if timed, milled, and manipulated just right, could produce a slowly animated sequence of images being projected by an otherwise empty window during different times of day.
To control the shape of a caustic pattern generated by a specular or refractive surface, we need to solve the inverse problem: how can we change the surface geometry, such that incident light is redirected to produce a desired caustic image?
Karen Terry's house in Sante Fe, designed by architect David Wright, is perhaps one of the most compelling passive designs.
Stepping down its hillside site in four tiers, it nestles low into the ground. Thick adobe sidewalls create a strong sense of shelter and its banks of windows look resolutely to the sun. The image is very much of a house attuned to sun and earth.
Rather than providing the convenience of a constant indoor temperature regulated by a thermostat, a passively solar-heated house may go through an air temperature flux as great as 20ºF per day. People learn to live with this flux.
Living in a solar house is a whole new awareness, another dimension. I have the comfort of a house with the serenity of being outdoors—protected, yet tuned in.