Movement under emergency lighting: the effects of changeover from normal lighting

Abstract

This paper considers how people's ability to move over an escape route is affected by different procedures for changing from normal room lighting to emergency lighting. The experiment took place in a large open plan office at two emergency lighting illuminances, 0.16 lx and 0.012 lx. The changeover to emergency lighting was either instantaneous or involved a 5 second period of darkness before the emergency lighting came on, as is allowed by BS 5266. The subjects were instructed either to move as soon as the emergency lighting came on or to wait until they felt able to move unhesitatingly over the escape route. The time taken to leave the office, the manner of movement and subjects' opinions of the conditions were all recorded. They showed that movement was faster, smoother and easier at 0.16 lx than at 0.012 lx, for all conditions. When the subjects moved immediately the emergency lighting came on, having a 5 second period of darkness allowed more rapid, steadier movement with fewer collisions once movement started. However, the total time taken to leave the room was slightly longer than if the subjects moved immediately following an instantaneous changeover. Allowing the subjects to wait until they felt able to move unhesitatingly, ensured smooth steady movement but the total time taken at 0.012 lx was much longer than if the subjects started to move immediately after the changeover. Estimates of the state of adaptation of the visual system following a step change in luminance provide a plausible explanation of all these results.