Design of anidolic zenithal lightguides for daylighting of underground spaces

Due to the congestion of contemporary large cities, the exploitation of the basement is strongly increasing. This is why, after subways and car parks, new public spaces like concert halls and auditoriums are getting common in downtowns' basements. For this kind of building typologies, where windows are inadequate and skylights unsuitable, zenithal lightguides can be used t o provide daylight. Their luminous performance can be improved by using sun light trackers or static concentrators, which generally reduce the incoming of daylight during overcast conditions. The theory of anidolic optics non- imaging optics), was used to overcome this difficulty. Scale models were us ed to assess their performances thanks to a scanning sky simulator. It was shown that the adjunction of an anidolic element to a plain zenithal lightg uide improves its luminous performance: it provides an optimal concentratio n of sunlight for clear sky and a moderate reduction of the illuminance for overcast conditions. User-friendly abacuses were set up to support the des ign of anidolic zenithal lightguides in practice, including the shaping and the dimensioning of the device. (C) 2001 Elsevier Science Ltd. All rights reserved.