Preferred luminance distributions in open-plan offices in relation to time-of-day and subjective alertness

Abstract

Dynamic lighting is one of the new trends in lighting research; providing the right lighting level at the right time could possibly increase the alertness and performance of office workers. However, they might have preferences that deviate from this "healthy" lighting. Simultaneously, the building environment becomes increasingly automated, with occupancy-based control as one of the most well-known examples to reduce offices' lighting energy consumption. Nevertheless, preferences for lighting levels in the unoccupied area of the multi-occupant office space have not been addressed yet. Therefore, we studied luminance distribution preferences in relation to time of day and subjective alertness (SA) in a single occupancy scenario. Participants (N = 30) set the surrounding and background lighting six times a day as we first probed for SA. Our results clearly showed that a subset preferred varying luminance distributions; participants had fluctuating feelings of alertness, too. Preferences deviated sometimes from the typical dynamic lighting scenarios, suggesting that they do not always prefer healthy lighting. Moreover, we identified an effect of SA on the preferences, both with and without controlling for time of day. Hence, this study showed that we need to address these two factors when we want to provide satisfactory lighting conditions in case the office is not fully occupied. These are likely to affect other lighting preferences and therefore deserve more attention from research. Because we identified large individual differences, we suggest personalizing dynamic scenarios as the focus of future research.

Flow of Light: Balancing Directionality and CCT in the Office Environment

“…They stressed the potential of combining direct and diffuse lighting to create the atmospheric perception people often relate to day-lit spaces. De Bakker et al (2019) studied luminance distribution preferences in relation to the time of day and subjective alertness, and they found that participants preferred varying luminance distributions. Veitch and Newsham (2000) recommended a mixture of direct and indirect ambient lighting, with approximately 40% being indirect.…”

An experiment of double dynamic lighting in an office responding to sky and daylight: Perceived effects on comfort, atmosphere and work engagement

“…21 studied luminance distribution preference in relation to the time of day and subjective alertness, and reported that participants preferred varying luminance distributions and they did not always prefer the same lighting, defined according to non-visual effects on increasing alertness and performance. 21 Studies of dynamic lighting have demonstrated a preference for dynamic lighting responding to unpredictable natural variations in weather and light levels. 8,22,23 These studies investigated the relationship of the distribution of the light in a space and a combination of daylight inflow from a window and electrical lighting in real space.…”