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

An efficient lighting control systems (LCS) should take advantage of the natural light available, but this presents some technical challenges as well as user related issues. So far, the assessment of lighting energy consumption of LCS has been based on technical features rather than the occupants’ acceptance. This article presents the results of a monitoring study providing some recommendations based on the human and technical aspects of LCS in small scale applications. Four identical peripheral office rooms located in Lund, Sweden, were equipped with four different LCS: manual switch at the door, presence detector, daylight dimming with absence detector and LED task lamp. Each occupant performed ordinary office tasks for two weeks in each room in April-May 2013. A subjective evaluation concerning the general lighting experience and the appreciation of the LCS was carried out. The results indicate that the manual switch with absence detector was greatly appreciated and it accomplished good energy performances (75% savings compared to the presence detector). The daylight-linked LCS achieved only slightly higher savings (79%), due to relatively high parasitic losses, but it did not guarantee an optimal light environment. The desk lamp achieved 97% savings, but the lighting conditions were considered unacceptable by the office workers. In general, the participants in this study perceived all automatic controls as stressful.