Even when the sun is below the horizon, daylight is present in the atmosphere. This paper presents an approach for determining daylight availability during twilight, using multiple regression models. These models were used to estimate the number of hours that require artificial public lighting. This study was conducted in the city of Belo Horizonte, Minas Gerais, Brazil, measuring the monthly period of illuminances availability. Global illuminance data were collected by the Daylight Measurement Station of Belo Horizonte (EMIN-BH). The analysis of night length, depending on the sky models and types, was done by applying the developed models to the types of sky characteristic for each month of the the year. The mean night duration measured was 11 hours and 30 minutes, while the predicted duration was 11 hours and 29 minutes, which indicates that the models developed were adequate.
Daylight availability; Twilight; Night duration
