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Stationary Lights are lights that are intended to stay in one position, but are able to change in other ways, such as their brightness and color. This is the primary way in which they differ from Static Lights, which cannot change in any way during gameplay. However, it should be noted that runtime changes to brightness only affect the direct lighting. Indirect (bounced) lighting, since it is pre-calculated by Lightmass, will not change.
Of the three light mobilities, Stationary lights tend to have the highest quality, medium mutability, and medium performance cost.
All of the indirect lighting and shadowing from Stationary Lights is stored within the Lightmap. Direct shadows are stored within the Shadowmap. These lights make use of Distance Field Shadows, meaning that their shadows can remain crisp even with fairly low Lightmap Resolution on lit objects.
Stationary lights support IES profiles, described in Example 3.1 ; and light functions, described in Example 3.2 .
Overlapping
Stationary Lights are limited to a maximum of 4 being able to overlap at one time. Once you have 5 or more Stationary Lights overlapping, the one with the smallest radius will start casting dynamic shadows, which have a higher performance cost. You will also get warnings when rebuilding your lights. Here you can see 5 Stationary Lights placed close to one another. Notice that the fifth has a red X over it, indicating that it is now casting dynamic shadows.
Light overlapping can also be visualized in Stationary Light Overlap mode, available within the Viewport's View Mode menu. This view mode shifts from green to red as you increase the number of overlapping Stationary Lights. Once you hit 5 and above, the scene turns red, indicating a problematic light. In the image below, the fifth, and problematic, overlapping light's radius is shown in red.
