Energy evaluation of dynamic circadian rhythm lighting

Our review of the circadian lighting systems showed a lack of daylight-responsive lighting controls in most cases assessed. Presence/occupancy detectors were installed in only a few cases. This had a substantial impact on lighting energy use, as electric lighting was switched on during periods during which it would not be necessary.

When we compared standard lighting installations with circadian lighting installations through energy calculations with actual operating hours and the installed power (W) of the lighting systems, we could show that the implementation of daylight-responsive control systems and presence detectors could save between 18 and 39 percent of the building’s energy for lighting. We presented comparisons between the actually installed circadian systems, standard lighting systems, and systems with the required and recommended daylight-responsive controls and presence/occupancy detection.

When analyzing the user surveys, we found that most staff users were generally satisfied with the circadian lighting system. At the same time, we observed a great deal of desire for better information and communication/education about the purpose and use of the circadian lighting systems by nearly all staff members in the institutions assessed.

We also investigated perceived spatial brightness when illuminating vertical or horizontal surfaces in a room. Test with calibrated virtual images showed that lighting vertical surfaces in a room – that then reflected light back into the room –allowed for lower illuminance levels (lux) on the horizontal plane (e.g. the floor) while still achieving the same perceived spatial brightness as with a reference scenario with direct lighting from downlights. We attribute this to the circumstance that vertical surfaces typically dominate our visual field, especially when seated or standing. This knowledge can be included in future studies and the ongoing development and design of circadian lighting.

To provide guidance to clients and designers wanting to establish circadian lighting systems in future buildings, we provided an overview of “best practice” solutions and recommendations based on our measurements and user surveys during the case studies, as well as the virtual lighting tests