Hosek-Wilkie (2012) — Analytic Sky and Solar Radiance
| Class | HosekWilkieSkyLight |
| Family | Environment shader (Sky + analytic shader) |
| Author(s) | Hosek, Wilkie |
| Year | 2012 |
| Reference | Hosek, L., Wilkie, A. (2012). An analytic model for full spectral sky-dome radiance. ACM Trans. Graph. (SIGGRAPH 2012) 31(4), 100:1–100:9. |
Introduction
The Hosek-Wilkie model improves upon Preetham by also accounting for ground albedo and by fitting the nine-parameter radiance function to a broader dataset of sky radiance measurements.
It uses a degree-5 Bernstein spline for the solar elevation dimension and bilinear interpolation over turbidity.
The model is available in RGB and full-spectral (380–720 nm) variants; GroIMP uses the RGB tables for real-time preview and rendering.
Parameters
| Parameter | Type | Range | Description |
|---|
| turbidity | float | 1 – 10 | Atmospheric turbidity. 2–3 = clear, 6–10 = hazy. |
| albedo | float | 0 – 1 | Ground albedo (fraction of reflected ground light). 0.1 = dark soil, 0.5 = snow. |
| sun | Vector3d | unit vector | Sun direction (y-up convention). |
| radianceFactor | float | > 0 | Global radiance scale factor. |
| disableLight | boolean | — | Suppress sky contribution. |
Renderer compatibility
| Twilight (Sunflow) | ✅ continuous sampling per ray |
| GPUFlux | ✅ pre-baked 512×512 importance-sampled environment map |
| OpenGL / Proteus | background colour only |
Notes
Compared to Preetham, Hosek-Wilkie produces more accurate horizon and circumsolar colours, especially at low solar elevations (sunrise/sunset). The ground albedo parameter noticeably brightens the sky dome near the horizon for bright surfaces like snow.