Investigation on the daylighting potential in low-latitude subtropical region under different control methods

Fluctuations of daylight can cause uncertainties in evaluating its accessibility for building design and optimization tasks by the time-averaged solar and daylight data in hourly interval. This study thus investigates the transient daylight fluctuations and their consequences on the electric light that operates under the typical dead-band and time-delay controlling methods for a hot and humid subtropical region. We quantified the duration and its occurrence probability of the electric lighting operation due to the daylight instability with typical lighting control methods, and its correlations with the weather condition. For the controlling methods under study, results show the instability-associated lighting duration ranges from 140 to 700 h per year. This length account for 3.84% to 19.18% of the office hours, and is comparable to the period length with indoor illuminance below 450 lx during the day. This operation length is expected to be highest in cloudy condition, roughly taking 100 min per day, much higher than the overcast and clear conditions with around 30–40 min. The temporal lengths per day under dead-band and delay methods are less than around 50, and 130 min for more than 80% cases. The findings are essential to the accurate evaluation of daylight performance in buildings especially for buildings with unstable and cloudy weather conditions.