2007 - Daylight Symposium
CLIMATE-BASED DAYLIGHT MODELLING FOR EVALUATION AND EDUCATION by John Mardaljevic
John Mardaljevic (UK)
Daylight Experts Ltd
The daylight factor method, established a half-century ago, is still the most commonly used approach to determine a quantitative measure for daylight in buildings. The limitations of the daylight factor are manifest. Because it is founded on illuminance ratios under a standard overcast sky, the daylight factor is insensitive to both the orientation of the building and any notion of climate. Nevertheless it persists as the dominant approach because of its familiarity and simplicity rather than as a reliable measure of daylight provision. Recently developed computer simulation techniques can accurately predict luminous quantities using realistic sun and sky conditions that are derived from standard meteorological datasets. These climate-based modelling approaches reveal the true daylighting potential of buildings and can be used to predict a variety of illumination metrics at all stages of the design evaluation process. The application of climate-based daylight modelling to a range of building evaluation scenarios is described in this presentation. Working closely with practitioners on these studies, it became evident that the climate-based analyses caused them to fundamentally reappraise their understanding of daylighting and its relation to the built form. The presentation closes with a discussion of the role of climate-based modelling in the teaching of architectural daylighting principles.
John Mardaljevic, BSc, MPhil, PhD, Institute of Energy and Sustainable Development De Montfort University The Gateway, Leicester, has a first degree in physics, an MPhil in astrophysics and a PhD in daylight simulation. His first significant contribution in the field of daylight modelling was the validation of the radiance lighting simulation program under real sky conditions. John Mardaljevic has proposed a new climate-based metric called ‘Useful Daylight Illuminance’ as a replacement for the daylight factor.