by Dr. John Mardaljevic, De Montfort University, UK

Abstract
A parametric climate-based analysis for two residential building types with various window configurations and external obstructions. Each of the ten building configurations was evaluated for all combinations of eight orientations and six climate zones. Thus there were 480 sets of unique climate-based daylight simulations. The evaluation was founded on the useful daylight illuminance (UDI) scheme which determines the occurence of absolute levels of illumination in four ranges: less than 100 lux; 100 to 500 lux; 500 to 2,500 lux; and, over 2,500 lux. The limits of these range are founded on human factors data from occupant surveys.

The key indicator for "good" daylighting is the degree of occurence of illuminances in the range of 500 to 2,500 lux (labelled UDI-a metric) since this range: provides adequate illumination for the majority of tasks; is associated with a very low probability for the switching-on of electric lights; and, the higher values in this range are now believed to have beneficial effects for both productivity and long-term health.

This study has shown that the addition of skylights invariably improves daylight performance of the space. For some designs, the addition of skylights led to a typical increase in the occurence of the key UDI-a metric from 12% to 45% of the occupied year (i.e. 08h00 to 20h00).

Supplementary reports documenting the simulations output are available, contact us for further information.