Beyond RGB Tristimulus: Continuous 6500K Solar Illuminant Simulation

For over three decades, computer graphics has relied on a foundational compromise: tristimulus RGB color spaces. By reducing the infinite-dimensional continuous spectrum of light into three arbitrary scalar values—Red, Green, and Blue—renderers sacrificed the physical reality of electromagnetic wave transport.

While RGB is sufficient for display output on liquid crystal or organic LED screens, it breaks down fundamentally inside light transport simulation.

The Metameric Failure of Tristimulus

In physical optics, two light beams that appear identical to human eyes under one illuminant can reflect entirely different colors under another. This phenomenon is known as metamerism.

When a renderer collapses light into RGB before computing material interactions:

1. Prism Rainbow Splitting is Impossible: Because a single RGB ray cannot divide into its constituent wavelengths without ad-hoc fake shaders.
2. Absorption Bands Disappear: Atmospheric Fraunhofer lines (the distinct dark absorption bands caused by solar oxygen and hydrogen) cannot be evaluated.
3. Fluorescence and Quantum Yield are Distorted: Energy transfer across wavelengths cannot be represented by a 3x3 matrix multiplication.

The Solis 81-Band Continuous Formulation

Solis replaces RGB vectors with an 81-element energy vector representing irradiance in 5nm bins across the 380nm–780nm human photopic window:

export interface SpectralPowerDistribution {
  minWavelength: 380;
  maxWavelength: 780;
  step: 5; // nm
  radiance: Float32Array; // 81 bins
}

By computing light transport across all 81 bins simultaneously within modern SIMD GPU registers, Solis computes optical reflections with zero metameric failure and mathematical repeatability.