Movement under emergency lighting: the effect of illuminance

Abstract

This paper describes an investigation carried out in a large open plan office with the aim of identifying the illuminance necessary for rapid, safe movement under emergency lighting conditions. In the experiment, the times taken for each subject to cover an escape route were measured. The manner in which the subjects moved was observed and their opinions of the conditions were noted. This data was collected from sixty subjects in all, twelve at each illuminance condition. The subjects were not familiar with the office and were of working age. From the data collected it is concluded that at a mean illuminance of 0.2 lx, people experience some difficulty in moving quickly and unhesitatingly over the escape route. At a mean illuminance of 1 Ix there is no difficulty in moving smoothly and steadily over the escape route at a speed similar to that achieved under the normal room lighting. These results suggest that the present emergency lighting criterion of a minimum illuminance of 0.2 Ix is only reasonable if it is indeed treated as an absolute minimum. They also indicate that it would be useful to adopt a mean illuminance of 1 Ix on the escape route as an additional emergency lighting criterion. Three subsidiary experiments were carried out to explore the effects of age, familiarity with the office and group movement rather than individual movement. These subsidiary experiments showed that these factors made little difference to the subject's ability to move under the emergency lighting. Therefore the conclusions reached for the main experiment also apply to older people of working age, to those who are familiar with the space and to people moving in small groups.