You don’t need to buy Nvidia’s RTXGI SDK. If you download (free to use until your game earns $1M), it comes with Lumen .
RTGI works by tracing the path of light as it bounces off different surfaces in a scene. This is achieved through complex algorithms that calculate how light interacts with various materials, simulating effects like diffuse interreflections, specular reflections, and even volumetric effects like light scattering through fog or clouds. rtgi free