Field study of office worker responses to fluorescent lighting of different CCT and lumen output

Abstract

A field study was performed to examine the effects of correlated color temperature (CCT) and lumen output of fluorescent lighting on office occupants' visual comfort, brightness perception, satisfaction, and self-reported productivity. Twenty-six participants were recruited (mean age = 38.8 years; age range = 23–55 years). Ten of them had daylight access in their personal work areas. Four lamp types were selected to create luminous conditions organized as a 2 × 2 factorial design, comprising two levels of CCT (i.e., 3500 and 5000 K) and lumen output (i.e., 2330 and ≈3000 lm). Each condition lasted two weeks. Under each condition, participants adapted during the first week. During the second week they completed ecological momentary assessments (EMAs) three times daily using smart phones. Two of the daily EMAs included questions about lighting. Participants also completed a web-based survey on the last day of each condition. The results from the EMA (60.0% response rate) and web-based (77.2% response rate) surveys were generally consistent, indicating that CCT significantly affected spatial brightness perception, visual comfort, satisfaction, and self-reported productivity. The luminous conditions at 5000 K (visually cooler) were rated to be brighter than those at 3500 K (visually warmer), especially when higher lumen output was in place. However, the increase in spatial brightness perception came with lower satisfaction, worse visual comfort, and worse self-reported productivity. The conditions at 5000 K were judged to be too cool, especially for those who had daylight in their work areas. The results of this study do not support the spectrally enhanced lighting (SEL) method advocated by the U.S. Department of Energy (DOE) as an energy savings strategy. Even when higher CCT resulted in higher spatial brightness perception, occupants' visual comfort and satisfaction were compromised.