The game doesn’t have any form of dynamic global Illumination, so Larian uses LightProbe to capture HDRI map around itself and then calculate and “bake” indirect lighting.

There are 2 types of light probes:

1. Distant probes are used to account for far away lighting information: the sun and sky.It uses the information of the surrounding atmosphere to apply an approximation of sun and sky light bouncing and color to everything in that atmosphere. Since the probe contains lighting information, it applies to everything in that LightingResources. You only need one distant probe per Lighting trigger.
2. Local probes are used to simulate color and reflections related to nearby lights and objects. Local probes only gather information within a defined area around them and thus, only apply to objects in that same area. Contrary to distant probes, you can place as many local probes as you want. Even probes inside other probe areas are allowed. The lighting of the smallest probes always gets priority over the lighting of a larger probe that covers the same area. With local probes, you fine-tune illumination and reflections where the distant probe, or a larger local probe proves to be insufficient.

Since I make levels mostly for one picture, I always use Distant one and then move it around to tune the lighting for my needs.

You should use Local for interiors and stuff, or to adjust some specific parts.

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A level must have at least one Distant light probe Do not edit Intensity. I think it does nothing in the actual game, haven’t really tested though

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Don’t forget that you can also change its size using Edit shape bounds tool (square with dots with a rhombus shaped square inside) in the tool bar

To render them, you need to select LightProbe and toggle forth and back Inifinite Capture or Enabled (I haven’t figure out a better consistent way) to update the lighting; you should see the changes immediately, and then you can save your level.

The difference between a level with correctly rendered LightProbes and one with incorrectly rendered:

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Incorrect

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Correct

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In the incorrectly-rendered level, there’s no indirect lighting, which results in harsh shadows.

Whenever you make changes with a probe, you need to save your level in order for the LightProbe to save the rendered HDRI maps !!! If you have a lot of LightProbes, EACH LightProbe will render the map for EACH LightingResources in the LightingTrigger, so rendering will take some time !!! You should mainly focus on 1-4 LightingResources, and when you are finished with the level, only then add additional LightingResources, and make the final render.

Why they are important?

Level has better and correct lighting. Gives you flexibility over controlling your lighting. Reflective materials need them to correctly reflect, with no light probes, these materials will be black.