A Overview of The Current State of Daylight Legislation

Abstract

Building codes and regulations are intended to safeguard the health, safety, and welfare of building occupants. Over the years, building illumination stan-dards have evolved due to the progress made in sci-ence and technology which has made lamps more en-ergy efficient and photometrically stronger. Because of such progress, design benchmarks have dimin-ished both in terms of illumination levels and espe-cially in terms of lighting energy consumption levels. But despite this progress, lighting still represents the lion share when it comes of energy consumption of large buildings. As published by the Electric Power Research Institute, in the United States an average of 37% of commercial electricity consumption is con-sumed by electric lighting system (EPRI, 1995). Daylighting can reduce not only electric energy used for lighting but also lower and displace peak-demand, and at the same time the cooling loads. Despite these substantial energy benefits, daylighting is not yet a mainstream energy saving strategy within the build-ing industry. Because of this, some of its proponents suggest that the argument for daylighting should no longer be based on its energy savings potential, be-cause it has not been a very effective one, but it rather should be made in terms its other important benefits, namely of health and well being (Boubekri, 2004). Daylighting legislation is still lagging behind, beset by many problems, some germane to the field of lighting itself, and others more specific to the na-ture of daylight as a source of illumination. One issue, relevant to the field itself is the question of the form in which visual performance standards ought to be expressed. Although we see things because of lu-minance contrast between the visual task and its background; yet current illumination standards are still based primarily on illuminance levels (Boubekri, 1999). There is increasing evidence suggesting that meeting illuminance requirements alone does not necessarily guarantee the success of a design solu-tion, and that illuminance should not be the only predominant requirement for assessing a lighting sit-uation. People seem to react more to luminance pat-terns than to illuminance levels (Henshell, 1990; Kinkeldey, 1990). There are other issues pertinent to the nature of daylight that make daylighting standardization a very complex undertaking. The spectral quality of day-light, which is difficult to duplicate artificially, make it an almost entirely different type of light source than any electric light source. Anecdotal evidence suggests, for example, that because of the superior characteristics and qualities of daylight, one might need less light with daylight than with electric light to perform the same visual task. This phenomenon is not completely understood however. The nature of daylight source further complicates standardization. It is dynamic, constantly changing in terms of inten-sity and color properties, unpredictable and unreli-able. This fact makes the requirement of certain daylight levels inside a room a complex issue. Though it is now possible to predict both exterior and interior day-light levels either through empirical or simulation modeling technique, such predictions are based on historical data, collected over a long period of time. But the data still remain only statistical predictions and, thus, cannot be guaranteed. Because of the dynamic nature of daylight, for illu-minance-based legislation must deal not only with il-lumination levels but also with their duration within a space. Legislation pertaining to daylighting has been expressed in several forms varying from one country to another. In this paper, we will review the various forms in which such legislation is expressed and dis-cuss the limitations of these forms of expression. Illuminance-Based Standards In the United States for example, the BOCA