Exit Portal



Table of contents:

Description:
This light type is an Exit Portal. An Exit Portal is a light that simulates an opening in an enclosed room, through which light from the outside can shine.

Usually, one would create a transparent surface and enable global illumination with a HDR backdrop. In that situation rendertimes can go up a lot, depending on the lighting setup. This is where Exit Portals come in handy: They light the scene just like an area light, but apply different color shading to it by looking up the backdrop color of the direction in which a sample ray goes. Consequently you can have global illumination-like lighting without actually enabling it and if you actually do enable it, you can concentrate and modify lighting to your needs (different falloff etc.).

Both images on the right are renders with only one Exit Portal (placement marked in red) and enabled GI (4 bounces) in an entirely enclosed room.
Example

Example


Settings:

Annotation:
The color setting of the regular light options tints the shading of the Exit Portal.
To make the Exit Portal double sided, go to the "Back" tab and click on "Enable".

Quality:
Sets the quality of the Exit Portal. The number of resulting samples is the square of this value.

Automatic Intensity:
If this option is enabled, the Exit Portal tries to choose a reasonable intensity setting. The intensity is affected by the size of the light and uses an inverse square falloff with a nominal range of 577.35mm.
In the form of an equation the intensity is defined as follows: Intensity = Width * Height * (0.57735 / Distance)^2

Note: The falloff setting of LightWave will be overridden, but the intensity setting can still be used to strengthen or weaken the resulting automatic intensity (in order to get the intended effect, leave it at 100%).

Mode:
Backdrop: Color samples will be taken from the current backdrop in the given Ray Direction (see below).

Spherical Map: A spherical map is used to look up the color in the given Ray Direction (see below).

Ray Direction:
Spot -> Light: The direction of the ray used to look up the backdrop color/spherical map comes from the shaded spot and goes towards the Exit Portal (standard setting, the Exit Portal acts like a window).

Light -> Spot: This is the reverse of the above ray direction. Basically the sample color comes from the direction of the shaded spot.

Image:
The image used for the mode "Spherical Map".

Image Seam Angle:
The seam angle used for the mode "Spherical Map".

Exit Portal