Kinetic Pictorial Art with Sun Spectra: My Heliochromic System

Leonardo, Vol. 14, No.4, pp. 295-296, 1981 Printed in Great Britain oo24-094X/81/040295-02$02.oo/0 Pergamon Press Ltd. KINETIC PICTORIAL ART WITH SUN SPECTRA: MY HELIOCHROMIC SYSTEM Jean-Pierre Charriitre* 1. My Heliochromic System is the product of five years of study of the subject of dispersed light and its application in kinetic pictorial art, Involved in this project were matters ranging from a review of the basic principles of optics to the design and use of precision electronic controls and electronic devices. I had decided early in the project to employ dispersed sunbeams to produce colors rather than to utilize light produced by other sources. (The use of electric lights in kinetic art has been discussed by numerous artists in past issues of Leonardo [I].) The reason wasthat not only does sunlight possess visible radiation of essentially all wavelengths, but it can be received in intensity limited only by the optical equipment used. Direct sunbeams from the Sun in a clear sky are required to produce a luminous range of saturated colors, of which a rainbow is only a pale example. Not even a color photograph can present the high saturation of the colors produced by the solar spectrum. P. K. Hoenich used sunlight in combination with filters to produce colored images on walls, but the saturation of the colors were limited by the use of filters [2]. In his more recent Robot Projector, sunlight passes through glass prisms as well as through colored filters and also is reflected from polished surfaces to produce images on an opaque mat white surface [3]. My Heliochromic System consists of four parts: (I) a heliostat (Fig. I), (2) a set of prisms (Fig. 2), (3) a parabolic mirror and (4) a Heliochromic Chamber. The heliostat is an instrument that by means of an automatically controlled flat mirror reflects a sunbeam in a prescribed direction, in this case to a set of prisms. The inclination of the mirror isadjustedon what in astronomy is called equatorial mounting. To do this one must take into account the latitude for each particular location of an installation. The heliostat automatic electronic control consisting of a set of nine photoelectric cells continually adjusts for changes in the altitude and azimuth of the Sun in its passage across the sky. Its operation ceases during the passage of a cloud, and it starts up again when the Sun reappears. The control can be maintained when the period of absence of the Sun does not exceedone hour. In so far as possible, the heliostat should face south and be placed at a location where there are no obstructions (trees, buildings, etc.) in order to benefit from sunlight from sunrise to sunset. *Kinetic artist, c/o Mr Boyer, 106 rue Casimir Ranson, 87000 Limoges, France. (Based on a text in French) (Received 9 Apr. 1980) 295 Fig. 1. View of the heliostat. Fig. 2. View of the set of water-filled prisms. The prisms are water-filled glass boxes having a triangular cross section for which two angles are 67.5° (Fig. 2). The set of prisms is supported on a mount that can be oriented precisely to receive the sunbeam reflected from the heliostat. The required angle of incidence ofthe sunbeam on the glass surface is governed by the index of refraction of the water. The prisms are aligned so that they receive in succession one beam from the heliostat. But light leaving each prism is dispersed in accordance with the angle presented by one face to the light it receives. The angle for each prism varies slightly from one to the next and the prisms are spaced adequately to produce a desired dispersion. In this way, spectra are produced in 296 Jean-Pierre Charriere which there are marked variations in brightness. I find it interesting to fix the positions of some prisms and to rotate the others through small angles to produce such variations. Light leaving the set of prisms passes to a parabolic mirror that has a focal distance ofat least 15or 20 meters in order to assure approximately parallel rays. In a permanent installation, the heliostat, the set of prisms and the...