Category: Light
Shader Type: Light
Output: Color (RGB) value
The Portal Light (mia_portal_light) shader is most often applied to a rectangular area light which is placed in the window of a room scene. The shader obtains its proper intensity and color from the sky outside the window (for example, an environment shader such as the Physical Sky shader or similar) and how much of that sky can be seen.
When used with final gathering, the Portal Light acts as a final gathering concentrator, so that instead of having to send thousands of final gather rays around the scene to “find” the window, the portal light actually blocks final gather rays, and instead converts light from beyond the window to direct light, including high-quality area shadows.
Final gathering will now see a well lit room rather than a black room, and can use much lower final gather ray counts. Furthermore, since the light from the window is now direct, you gain one extra light bounce for “free”.