Long-term visual quality evaluations correlate with climate-based daylighting metrics in tropical offices – A field study

In this paper, we present a post-occupancy study of 326 participants in 10 daylit office buildings in Singapore and correlate the results with climate-based daylighting metrics and electric lighting simulations using calibrated simulation models of the 10 buildings. For the first time, this study tests the climate-based daylighting metrics which are used in building design against their impact on occupant perception within buildings. We find significant correlations between climate-based daylighting metrics and reported occupant satisfaction with access to daylight, view interest, perception of ‘too low’ lighting levels and visual comfort. Overall, climate-based daylighting metrics which account for lower illuminance thresholds such as continuous daylight autonomy and useful daylight illuminance combined (100–3000 lx) correlate more strongly with subjective results than do electric lighting sufficiency metrics such as daylight autonomy at 300 and 500 lx thresholds. Simple descriptive statistical representations of annual daylight distributions, mean and median annual daylight illuminance values, outperform climate-based daylighting metrics in correlation strength and p-value. Based upon these results, new metrics are proposed for occupant satisfaction with daylight access and views. In addition, increased daylight levels are shown to decrease reporting of lighting levels being ‘often too low’ even when adequate electric lighting is provided, and contrast is likely to be beneficial to space perception at non-glaring thresholds.