The objective of this document is to promote the use of dynamic daylight performance measures for sustainable building design. The paper initially explores the shortcomings of conventional, static ...

This paper introduces a new paradigm to assess daylight in buildings called ‘useful daylight illuminance’, or UDI. The UDI paradigm preserves much of the interpretive simplicity of the conventional daylight factor approach. In contrast to daylight factors however, UDI is founded on an annual time-series of absolute values for illuminance predicted under realistic skies generated from standard meteorological datasets. Achieved UDI is defined as the annual occurrence of illuminances across the work plane where all the illuminances are within the range 100-2000 lux. These limits are based on reports of occupant preferences and behaviour in daylit offices with user-operated shading devices. The degree to which UDI is not achieved because illuminances exceed the upper limit is indicative of the potential for occupant discomfort. The relation between achieved UDI and annual energy consumption for lighting is examined.

The drive towards sustainable, low-energy buildings has increased the need for simple, yet accurate methods to evaluate whether a ‘daylit’ building meets minimum standards for energy and human comfort performance. Current metrics do not account for the temporal and spatial aspects of daylight, nor of occupants comfort or interventions. This paper reviews the historical basis of current compliance methods for achieving daylit buildings, proposes a technical basis for development of better metrics, and provides two case study examples to stimulate dialogue on how metrics can be applied in a practical, real-world context.

The illuminance predictions from the lighting simulation program RADIANCE are compared with measurements taken in full-scale experimental rooms under real sky conditions for both overcast and clear skies. Results are presented for clear glazing and two types of light shelf. The model sky description is based on the real sky luminance distribution measured by a sky luminance mapping instrument. The sky luminance and room illuminance measurements are simultaneous allowing an extremely accurate representation of the real conditions in the model. Model representation of the measured sky brightness distribution is described.