Advanced Lighting Techniques

Module 1: Advanced Lighting Techniques 

1. Physically Based Lighting

Physically Based Lighting (PBL) simulates how light behaves in the real world, ensuring consistent material interactions under different lighting conditions.

• HDRIs & Image-Based Lighting (IBL)

• Definition: High Dynamic Range Images (HDRIs) are 360° environment maps that capture real-world lighting data.

• Usage: Used as a primary light source in IBL, providing realistic reflections and diffuse illumination.

• Advantages: Eliminates manual light setup; offers natural falloff and color bleeding.

• Limitations: Static lighting (unless animated); may require tweaking exposure/rotation.

• Area Lights vs. Emissive Surfaces

• Area Lights: Simulate soft, realistic shadows (e.g., fluorescent panels, windows).

• Pros: Controllable intensity/falloff; optimized for rendering.

• Cons: Higher computational cost than point/directional lights.

• Emissive Surfaces: Geometry that emits light (e.g., LED screens, neon signs).

• Pros: Integrates with GI; good for complex shapes.

• Cons: Requires high samples to reduce noise; less intuitive control.

• Light Portals & Importance Sampling

• Light Portals: Guide render engines to prioritize light from openings (e.g., windows), reducing noise.

• Importance Sampling: Optimizes render calculations by focusing on bright light sources first.

2. Global Illumination (GI) Methods

GI simulates indirect light bounces, crucial for realism.

• Ray-Traced vs. Baked GI

• Ray-Traced GI: Calculated in real-time or at render time (e.g., path tracing).

• Pros: Accurate dynamic lighting.

• Cons: Slow for complex scenes.

• Baked GI: Precomputed (e.g., lightmaps in Unity/Unreal).

• Pros: Real-time performance.

• Cons: Static lighting only.

• Photon Mapping vs. Radiosity

• Photon Mapping: Traces light particles (photons) for caustics and complex bounces.

• Radiosity: Diffuse light transfer via mesh subdivision (older method, mostly replaced).

• Real-Time GI Solutions (Lumen, Enlighten)

• Lumen (Unreal Engine 5): Dynamic GI using software/hardware ray tracing.

• Enlighten: Precomputed + real-time hybrid (used in Frostbite games).

3. Volumetric Lighting & Fog

Adds depth and atmosphere by simulating light interacting with particles.

• Participating Media (Fog, God Rays)

• Fog: Scatters light uniformly, creating depth haze.

• God Rays (Crepuscular Rays): Visible light beams through occlusions (e.g., clouds, trees).

• Volumetric Shadows & Scattering

• Shadows: Light blocked within volumes (e.g., smoke casting shadows).

• Scattering: Types:

• Rayleigh (blue sky effect).

• Mie (hazy/foggy glow)
  

Key Takeaways:

• PBL relies on HDRIs and precise light types for realism.

• GI balances accuracy (ray tracing) vs. performance (baking).

• Volumetrics require careful tuning to avoid render overhead.