Evaluation of Sky Luminance and Radiance Models Using Data of North Bangkok

Abstract

The tropical sky is highly luminous. This gives rise to expectation of its high potential for daylighting. The availability of an accurate luminance distribution for daylight from the sky would help advance the movement for daylighting. On the other hand, accurate radiance distribution model is also needed to help manage the undesirable heat gain due to solar radiation penetration in air-conditioned buildings. Towards these ends, eight luminance and radiance distribution models were evaluated against luminance and radiance measurements recorded in a station located north of Bangkok. Due to prevalence of intermediate and cloudy sky conditions in the tropical region, attention was paid to seeking models that could perform well under these conditions. It turns out that a number of models are acceptable, but no single model performs distinctively well for the prevalent conditions.

Keywords:

• sky luminance and radiance distribution
• sky ratio
• mean bias difference
• root mean square difference