Perez All-Weather Sky
| Class | PerezSunSky |
| Family | Discrete light array (73 Turtle-geometry directional lights + sun) |
| Author(s) | Perez, Seals, Michalsky |
| Year | 1993 |
| Reference | Perez, R., Seals, R., Michalsky, J. (1993). All-weather model for sky luminance distribution — preliminary configuration and validation. Sol. Energy 50(3):235–245. |
Introduction
The Perez all-weather model distributes sky luminance among 73 directional lights using measured Diffuse Horizontal Irradiance (DHI) and Direct Normal Irradiance (DNI).
Solar position is computed from geographic coordinates (latitude, longitude), day-of-year, and hour via the Goudriaan algorithm.
The model covers the full range from overcast to clear sky and can be driven by real meteorological station measurements.
Parameters
| Parameter | Type | Range | Description |
|---|
| DHI | double | 0 – 600 W/m² | Diffuse Horizontal Irradiance — sky dome contribution. |
| DNI | double | 0 – 1000 W/m² | Direct Normal Irradiance — solar beam contribution. |
| latitude | double | −90 – 90 ° | Geographic latitude of the site. |
| longitude | double | −180 – 180 ° | Geographic longitude of the site. |
| dayOfYear | int | 1 – 365 | Day of year (1 = 1 January). |
| hour | double | 0 – 24 | Solar time (decimal hours). |
Renderer compatibility
| Twilight (Sunflow) | ✅ |
| GPUFlux | ✅ |
| OpenGL / Proteus | ✅ |
Notes
DHI and DNI can be obtained from meteorological databases (e.g., DWD, PVGIS, TMY datasets). Typical clear-sky midday values at mid-latitudes: DHI ≈ 80–150 W/m², DNI ≈ 600–900 W/m².