The archetype of dispersed light occurs when the wavelengths or colours of light that combine to produce sunlight are visibly separated, isolated, or selected. These effects can occur due to a variety of optic phenomena, but can most commonly be observed by way of dispersion, when the effects of minor variances among the indices of refraction for shorter wavelengths (such as blue light) and longer wavelengths of light (such as red light) are exacerbated. Because the indices of refraction increase or decrease alongside an increase or decrease in the wavelength of incident light, the paths of various wavelengths are bent to a greater or lesser degree as they pass through different media (per Snell's law).1 This effect is significant in the engineering of optical instruments whose operation depends upon refraction, (2) but is often only visible in architectural settings when the geometry of the medium (generally glass) that light passes through exaggerates the effect. When one uses a triangular prism to disperse light, the effect is observable because different wavelengths of light will continue to travel in different directions upon exiting the prism. In the case of a prism with parallel sides, the various wavelengths of light will be inversely dispersed at the second surface and will therefore continue on in the same direction with little evidence of any separation of wavelengths.
Architecture can facilitate the production of this archetype through the geometry of glass and glass-like materials. The effect commonly occurs when the edges of glass architectural artifacts are beveled, creating prisms. If the prism is stretched, the effect will diminish as the two planes become increasingly parallel. The archetype therefore has the greatest potential for impact through small or arrayed instances. This limitation can be circumvented through the use of dichroic filters. These materials are typically polymers that absorb much more light in one linear polarised state than the other perpendicularly oriented state. As Duree describes, this "process of selective absorption is very much dependent on the wavelength of the light."3 James Carpenter uses dichroic films in his 1995 facade project, Dichroic Light Field. The dichroic film on each of the two hundred and sixteen fins that project from the mirror-like screen transmits one half of the visible light spectrum while the other half is reflected.4 This polarisation of light provides the means by which to achieve a variation of the archetype, and deploys it in combination with the specular image archetype to register ambient lighting conditions while simultaneously operating on incident light.
1. Duree, Optics, 50.
2. Ibid., 54.
3. Ibid., 109.
4. Sandro Marpillero, James Carpenter Environmental Refractions (Basel: Birkhäuser, 2006), 41.