During the rendering process, daylighting is performed automatically. For advanced lighting quality in interior views, you can enable daylight portals, if needed. Daylight portals improve the quality of light that shines through windows, doors that contain windows or glass, and curtain walls.
Rendered image without daylight portals
Rendered image with daylight portals
Daylight portals are useful only for interior views that include sunlight. That is, on the Rendering dialog, under Lighting, the selected Scheme must be Interior: Sun only, or Interior: Sun and Artificial. (See Controlling Lighting in a Rendered Image.)
By default, daylight portals are turned off. If a rendered image shows sunlight reflecting off surfaces, and the sunlight is speckled or splotchy, you may be able to improve the image by turning on daylight portals.
To turn on daylight portals for an interior view that includes sunlight, use the Render Quality Settings dialog. See Define a Custom Render Quality and Advanced Render Quality Settings Reference.