Impact of daylight saving time on lighting energy consumption and on the biological clock for occupants in office buildings

Nowadays, there is an in-depth debate about the suitability of daylight saving time. The shift of one hour during summer time allows a better use of daylighting reducing energy consumptions. However, the impact of daylight saving time on the human health has not been quantified in most of the scenarios. The aim of this study is to determine the impact of daylight saving time on the health of occupants (by calculating Circadian Stimulus Autonomy) and on the energy consumptions for lighting (by calculating Daylight Autonomy) in office buildings. A standard office is analyzed in eleven representative locations of Europe and for three different time schedules: with daylight saving time, with continuous winter time and with continuous summer time. Despite restricted to a specific case study, results provide elements useful to evaluate pros and cons in maintaining daylight saving time, confirming that they are strongly dependent on the geographical position and on the local luminous climate. It was demonstrated that, abolishing daylight saving time, maintaining the local time all the year (winter time), would determine a reduction of Daylight Autonomy generally lower than 6% and that this decrease would be more consistent for cities characterized by higher latitude. At the same time an increase of Circadian Stimulus Autonomy values would be obtained, more consistent for northern cities (maximum observed increment 16%). On the other hand, applying the one-hour shift for the entire year (summer time) would not determine benefits in terms of energy savings nor of impact on circadian system.