Daylight availability and lighting use: Geographical variations

Within the UK, regional variations in climate and latitude (1,2) can cause differences in the relative amounts of daylight available; yet existing methods for predicting daylight in interiors are mainly based on daylight data from south-east England. There is increasing interest in using daylight to save lighting energy in buildings; however, it is possible that the benefits of daylighting may vary significantly from region to region throughout the UK. This paper reports on a study of the magnitude of this variation in lighting energy use, based on the model of manual switching in daylit spaces derived by Hunt (3,4) . Analysis of meteorological daylight data (5) for five locations has produced, for the first time, curves which can be used to predict hours of use of manually controlled lighting in daylit buildings in various parts of the UK. These curves are presented, together with an analysis of the regional differences in lighting use for various example situations. The significance and probable causes of these variations are discussed, and the need for more daylight measurements in different parts of the country is explored.