06.11.2023 – Lighting

Week 6 – Lighting in Unreal Engine

In Unreal Engine, achieving realistic lighting is crucial for creating immersive scenes. Light Actors play a significant role, and their mobility options dictate their behavior during a light build, influencing how they interact with the environment and how the lighting system utilizes them.

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Lighting

There are three primary Light mobility options:

• Static (Baked): Cannot be moved or updated during runtime. Precomputed using Lightmass, storing Lightmaps in their data. Offers medium quality, the lowest performance cost, and fast rendering.
• Stationary (Hybrid): Does not change position, but certain properties like color and intensity can be modified. Allows partial baked lighting with a limitation of up to 4 overlapping lights. Stores indirect lighting and shadowing within lightmaps, providing high quality, medium performance cost, and nice Global Illumination (GI) and animated shadows.
• Movable (Dynamic): Can be changed in every property during runtime. Utilizes Lumen for dynamic light and shadows. Offers varying quality depending on dynamic shadow usage, the highest performance cost, and the slowest rendering.

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Various types of lights are available:

• Point Light: Used for bulbs or lamps.

• Spot Light: Suitable for theatrical lighting, ceiling lights, and focused lighting.

• Rect Light: Ideal for ray tracing, acting as fill lights to simulate board reflectors, screens, and backlit billboards.

• Directional Light: Used for primary outdoor lighting or any light that needs to appear as if casting light from extreme distances.

• Sky Light: Provides image-based ambient light, lighting shadowed parts of the scene, and captures a 360-degree image from the sky.

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In addition, these actors allow you to fine-tune the atmosphere of your scene:

• Sky Atmosphere: This actor provides a physically-based rendering effect for the sky and atmosphere. It includes its own scattering and height fog simulation, complementing the Exponential Height Fog. The two types of light scattering it employs are Mie and Rayleigh. Mie scattering, occurring with dust, smoke, and water drops, happens when large particles scatter all wavelengths of white light equally. Rayleigh scattering, observed with shorter wavelengths (violet and blue) of visible light, adds another layer of realism.
• Volumetric Cloud: This actor utilizes a material-driven approach to create a physically-based cloud rendering system, offering the flexibility to generate various types of clouds.
• Exponential Height Fog: This actor enhances the scene by creating varying fog density in low and high places on the map. The transition is smooth, eliminating a hard cutoff as altitude increases. Additionally, it provides options for two fog colors, allowing for nuanced environmental adjustments.

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When assessing the lighting in your project, consider utilizing the following tools:

• Macbeth Chart: This tool allows you to inspect the shape of light, intensity, or changes by adjusting options on chrome and grey balls.

• Env. Light Mixer: Use this tool to check every light in the level, providing a comprehensive overview of the lighting elements.

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Global Illumination

Unreal Engine offers two types of Global Illumination (GI):

• Baked and Pre-Computed (GPU Lightmass): Set mobility to Stationary or Static. This method requires the baking of lighting maps, demanding a substantial amount of memory. It inherently supports Static Mesh and DSP geometry.
• Dynamic and Real-Time (Lumen): Set mobility to Movable. This approach supports movement and interaction in real time, ensuring lighting updates with each frame. Ideal for expansive environments, it inherently supports all geometry types.

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Post Process Volume

You have control over the areas affected by the Post Process Volume (PPV) in your Level. If multiple PPVs overlap, you can prioritize their influence and manage how they blend with each other. To apply a PPV to the entire Level, enable ‘Infinite Extent (Unbound).’