Rethinking daylighting and compliance

Daylight in buildings is the natural illumination experienced by the occupants of any man-made construction with openings to the outside. Our attempts to formulate some measure of daylight provision in buildings can be traced back over a century, and the daylight factor as we know it today is over 50 years old. Still the most common measure found in guidelines and recommendations worldwide, the daylight factor is used routinely and, it is fair to say, often rather uncritically. The consideration of daylight in buildings has received a new impetus from the accumulation of evidence on the wider benefits of daylight exposure. But it is continuing to prove difficult to advance beyond daylight factors towards a more realistic quantification of daylighting performance that would allow us to accommodate these new considerations in an evaluative schema. This paper examines the basis of current practice with respect to daylight evaluation, and suggests a few ways in which it can be improved with relatively modest additional effort. The paper also critiques some of the recent attempts to advance daylight evaluation by incremental means using so-called “clear sky options”.