I've been experimenting with Blender's new Eevee engine over the past couple of days and, so far, have failed to get the realistic results I'm aiming for. I've seen some online tutorials and articles about the assets under the new "Light Probes" category in the add menu, but I'm still not quite understanding what they do and how I'm supposed to work them. There are minimal tutorials out there and not a single one of them (at least the ones I've seen) take a second to explain how to use them nor how they work.

enter image description here

There's three options under the category: Reflection Cubemap, Reflection Plane, and Irradiance Volume.

All I'm asking for is a breakdown on what each of these items do, how to use them, and in what situations they're appropriate to apply them to. Thanks!

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    $\begingroup$ This is a good question, and you did a great job presenting it. Good work! $\endgroup$ – TARDIS Maker Jan 9 '19 at 7:02

There are three types of Light Probes

  • Reflection Cube Map
  • Reflection Plane
  • Irradiance Volume

Reflection Probes

The two first are, as the name suggests, to generate reflections for materials. They may seem useless at first because you can enable Screen Space Reflections in EEVEE render panel, however screen space reflections have limitations. They are very fast to generate, but can only capture objects that are currently displayed in the viewport, that is inside the view fustrum.

These probes allow calculation more complex and accurate types of reflection through use of a helper object (the probe).

Reflection Plane

As the name suggests Reflection Plane are the most simple ones, suitable for mostly flat surfaces like mirrors, glass panes, floor reflections, or rainy pavements. On more complex objects they will probably generate weird results.

It has a clipping distance that will limit which objects are visible in its reflections. They are relatively cheap in terms of computation and don't require baking.

Objects with reflective materials that reside withing its range (the bounding box around it) will be influenced by what this plane "sees", benefiting from the the probe reflection map.

enter image description here

Reflection Cube Map

Similar to the plane this will generate a more complex reflection map suited for curving shapes. Unlike the plane though this is not a real time process and requires baking, specifically the Bake Cubemap Only option from the Render Panel in the Properties Editor.

It also has clipping distances which affect the range of what is reflected and what gets clipped away. Moving a reflective object away from its influence radius also removes it from it's "effect".

Cube map influence range

Irradiance Volume

Irradiance Volume is a different kind of probe, it calculates indirect lighting and shadows rather than reflections. Real time rasterization engines like EEVEE although very advanced can't really calculate indirect lighting by themselves, thus need a help generating and displaying this information.

Irradiance Volume preform both these tasks by storing the indirect lighting information in a grid array of points, the resolution of which can be adjusted from its Resolution XYZ in Object Data Properties.

Once again Clipping affects which objects are in range for calculation, and everything inside its volume gets influenced by the light calculation.

Likewise, since this is potentially heavy calculation it requires baking from the render panel to show it's influence. The higher the XYZ resolution the denser the grid, the heavier the calculation thus slower process, with the resulting higher quality effects.

enter image description here

Common workflow:

  1. Add probe object
  2. Adjust position
  3. Scale it so it encompasses all desired parts of the scene
  4. Adjust clipping distances and grid density as desired
  5. Bake (from render panel for Cube Maps and Irrandiance Volumes)

These calculations should be stored within the Blend file and available next time you load it, so you aren't required to bake again.


Here are the results of the various bake steps

No Bake enter image description here

Cube Maps only (no indirect lighting, notice the reflections) enter image description here

Bake indirect lighting (notice the color bleeding, softer lighting, and proximity shadows) enter image description here

You may use several probes per scene to get denser details where required, but each one consumes memory and has a performance penalty on the viewport, so use them wisely.

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    $\begingroup$ Yes! Thank you! This was way more than I was expecting but it helps a ton. I appreciate the time you put into this $\endgroup$ – Squirrel Jan 9 '19 at 0:22
  • $\begingroup$ I love the explanation. Thankyou kindly for showing.. I have upvoted for you . $\endgroup$ – ToxsickcitY Aug 8 '19 at 6:04

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