Lighting control systems in individual offices at high latitude: measurements of lighting conditions and electricity savings

This paper presents measurement results of electricity use and lighting conditions in individual office rooms located in Lund, Sweden. The aim is to demonstrate the energy saving potential by using different lighting systems and the satisfaction of users. The measurements are carried out in one empty reference room and four fully occupied test rooms equipped with different electric light control systems. The tested systems include: a presence detector (automatic switch on/off), a manual switch at the door combined with absence detector (automatic switch off), a photoelectric dimming combined with presence detector, and a switchable task light with no ambient lighting except daylight. The four rooms are fully occupied by test persons performing their normal computer-based tasks, and who make a subjective evaluation of lighting conditions in the room and control system once a week. The results for the first monitoring period show that the automatic switch on/off (presence) system is the one yielding the highest electricity use, which repeats earlier simulation results. The photoelectric dimming system which combines a presence detector yields very modest energy savings compared to the presence detector system, a result which contradicts earlier findings but which may be explained by malfunctions and poor sensor position. The room with the task lamp achieves the lowest energy use, which is mostly attributed to the low levels of illumination in the room, which is further confirmed by the test persons. The system with manual switch at the door combined with absence detector achieves the best results in terms of combined low energy use and user satisfaction, and the magnitude of the savings are generally greater than anticipated in earlier simulation studies achieved in the same context.