DESIGN AND ASSESSMENT OF AN ANIDOLIC LIGHT-DUCT

The system presented here, called Anidolic Ceiling, was developed to s how the viability of intensive use of daylight by overcast outdoor con ditions in nonresidential buildings. This device consists of a light-d uct that is integrated in a suspended ceiling and leads midway into th e office. Anidolic (nonimaging optics) elements are placed on either e nd of the duct, on the outside to collect light rays from the sky and on the inside to control the direction of the emitted light. The prese nt paper describes the system design, as well as an experimental asses sment of its daylighting performance in a comparison of a prototype an d a full-size conventional facade, for a 6.6-m deep room. Measurements by overcast sky have established that the daylight factor on the work plane 5 m from the window is more than doubled. In addition, a monito ring campaign has shown that 30% of the energy for lighting can be sav ed. The system was also assessed with regard to the user. Visual comfo rt measurements (Laboratoire d'Ergonomie de la Vision's (LEV) method) were carried out showing that for both clear and overcast outdoor cond itions, the visual environment quality is objectively improved at the rear working place. Furthermore, 33 people tested both rooms one after the other. They were submitted to a series of visual acuity tests on printed paper and on a computer screen and had to fill in a questionna ire. A comparative study showed that the personal appreciation of the luminous environment is better in the room with an Anidolic Ceiling, w ith a significant reduction of reading errors both on paper and on the screen. (C) 1998 Elsevier Science S.A. All rights reserved.