This page introduces you to how lighting works in Unity.
Lighting in Unity works by approximating how light behaves in the real world. Unity uses detailed models of how light works for a more realistic result, or simplified models for a more stylized result.
Direct light is light that is emitted, hits a surface once, and is then reflected directly into a sensor (for example, the eye’s retina or a camera). Indirect light is all other light that is ultimately reflected into a sensor, including light that hits surfaces several times, and sky light. To achieve realistic lighting results, you need to simulate both direct and indirect light.
Unity can calculate direct lighting, indirect lighting, or both direct and indirect lighting. The lighting techniques that Unity uses depends on how you configure your Project.
Real-time lighting is when Unity calculates lighting at runtime. Baked lighting is when Unity performs lighting calculations in advance and saves the results as lighting data, which is then applied at runtime. In Unity, your Project can use real-time lighting, baked lighting, or a mix of the two (called mixed lighting).
For information on configuring Light components to contribute real-time, baked, or mixed lighting, see Light Modes.
Global illumination is a group of techniques that model both direct and indirect lighting to provide realistic lighting results. Unity has two global illumination systems, which combine direct and indirect lighting.
The Baked Global Illumination system comprises lightmapping, Light Probes, and Reflection Probes. All render pipelines support the Baked Global Illumination system. Render pipeline support for each feature in the Baked Global Illumination system is indicated in the documentation for that feature.
The Realtime Global Illumination system comprises Realtime Global Illumination using Enlighten, and adds additional functionality to Light Probes. The Built-in Render Pipeline supports Realtime Global Illumination. The High Definition Render Pipeline (HDRP) and the Universal Render Pipeline (URP) do not support the Realtime Global Illumination system. Note that Enlighten is deprecated, and the Realtime Global Illumination system will soon be removed from Unity. For more information, see the Unity blog.