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Sunlight
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What happens to light?
100% absorbed
ฯโ = absorption
ฯโ = scattering
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Rayleigh Wavelength Response (ฯ โ 1/ฮปโด)
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Phase Function (where light scatters)
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Why is...
Rayleigh scattering! Air molecules are tiny (~0.3nm), much smaller than visible light wavelengths (400-700nm).
Blue light (ฮป=450nm) scatters 5.5ร more than red (ฮป=700nm) because ฯ โ 1/ฮปโด.
When you look at the sky, you're seeing scattered sunlight - mostly blue!
๐ Click "Atmosphere" preset to see this
๐ Click "Atmosphere" preset to see this
Mie scattering! Cloud droplets are large (~10-20ฮผm), comparable to light wavelengths.
At this size, all wavelengths scatter equally (no color preference), so clouds appear white.
The droplets are also highly forward-scattering (g โ 0.85), creating bright edges when backlit.
๐ Click "Cloud" preset to see this
๐ Click "Cloud" preset to see this
Long path through atmosphere! At sunset, sunlight travels through much more air.
Blue light gets scattered away along the path, leaving mostly red and orange to reach your eyes.
This is the same Rayleigh scattering - just with more distance for blue to scatter out.
๐ Click "Sunset Path" preset to see this
๐ Click "Sunset Path" preset to see this
The 3 Building Blocks of Light Transport
Absorption (Beer-Lambert)
Light gets absorbed and converted to heat. Different wavelengths absorb at different rates, giving materials their color.
T = e-ฯaยทdRayleigh Scattering
Particles much smaller than light wavelength (~0.1-1nm). Blue scatters 5.5ร more than red. Why the sky is blue!
ฯs โ 1/ฮป4Mie Scattering
Particles similar to light wavelength (~1-10ฮผm). All colors scatter equally โ white appearance. Why clouds are white!
ฯs โ constant
Light Source
#fff8f0
Absorption Coefficients (ฯโ)
Per-wavelength absorption (mโปยน)
Scattering Properties (ฯโ)
Particle Physics
Real-World Presets
๐ Physical Values (Current)
Extinction (ฯt = ฯa + ฯs)
0.52 mโปยน
Scattering Albedo (ฯ = ฯs/ฯt)
0.00
Mean Free Path (1/ฯt)
1.92 m
Optical Depth (1m)
0.52