Acceptable illumination levels for office occupants

This study examined the acceptable horizontal illumination levels in an office environment by interviewing 293 occupants about the visual environment being perceived in all classes of office buildings in Hong Kong. In particular, the measured horizontal illumination level (lux) in the offices was chosen as an indicator and correlated with the occupants' acceptability on a visual analogue assessment scale and a dichotomous assessment scale. The results showed that the occupants' acceptability was significantly influenced by the horizontal illumination level and was correlated with a logistic regression model. A satisfaction criterion of the lighting level was then evaluated from the frequency distribution of the occupants' response at certain horizontal illumination levels, and provided a measure to balance the occupants' acceptability and the energy consumption of the lighting system in the office area. In addition, the survey samples of the proposed criterion of visual comfort showed that an indoor environment with a horizontal illuminance of 518 lux would satisfy most of its occupants, corresponding to an overall satisfaction of 86%. This confirmed the design criterion (500 lux) generally adopted in current practice.