Lumen – Issues and Suggestions – Who’s with me?

First off, just wanted to let the devs know that Lumen is a huge step forward and an amazing attempt to achieve the holy grail of realistic GI in realtime. So I’m coming from a place of praise and hope to better this already amazing system.

With that said, let’s look the gift horse in the mouth and go over at the issues (at least the ones I’ve spotted and/or don’t know the work-arounds yet).

Virtual Shadow Maps (beta)

  • Though these work excellently for point / spot / rec lights. When used with a directional light I’ve found that the resulting penumbras creep under and through surfaces like walls. So for example in my scene I’m wanting to emulate an overcast day outside, so the sun isn’t pin sharp but diffused. This results in the below effect.


  • It’s great to see these being calculated by Lumen, but at the moment the ‘Indirect Lighting Intensity’ slider seems to have no effect, so we’re stuck at a fixed contribution level for now. Would be great to see this slider having an effect. I’m using a dull overcast sky, so I could really do with pumping the bounced light in occluded areas without making the direct light outside blown out.

Volumetric Fog
This is the real sore spot for me particularly, but I can image as most people use vol fog to create some kind of ambience in their scenes, it’ll effect a lot of people.

  • As far as I know there are no controls that relate to how Lumen interacts with your vol fog volume, it’s completely doing its own thing regardless of other sliders and switches you set elsewhere. And that ‘thing’ can get quite weird – see below. This is from just one directional light in the level; I’ve got bizarre streaks of light in the sky emerging from places where there’s no models or light sources. Also you can see the fog illuminance starts at about 2 meters above the ground for some reason.

  • Each light you place in the level comes with a ‘Volumetric Scattering Intensity’ slider that used to allow you to control the contribution of that light to the fog volume. They still work for the direct light cast, but, even if you set that slider down to ‘0’ Lumen ignores it and continues to propagate the light in the fog. I think there are two features that would be great here, ideally both, but one or the other would work.
  1. A slider that defines Lumen’s global contribution to vol fog, whilst leaving light’s direct fog contribution intact.
  2. A ‘GI Volumetric Fog Scattering’ slider alongside the existing slider (which now becomes ‘Direct Volumetric Fog Scattering’). The reason for the separation would be to allow a directional light to illuminate fog outside directly, and to be able to control the illumination of fog in the bounced light.
  • Emissives would also really benefit from the vol fog contribution slider / node in the material editor given that they have become more like regular lights via Lumen. In the shots below I’m using emissives to push light into a room, but when I turn on my vol fog the whole room become swamped in fog. So the ability to control that contribution would be much appreciated.


  • I also notice that emissives that update their material properties in realtime (colour or brightness for example) are often not reflected in Lumen’s GI. I’m presuming that’s because Lumen is doing it’s best to cache the output of lights.

Material Nodes

  • I expect this is coming further down the road, but the inclusion of material nodes that allow us to send different things to Lumen vs. the final raster would be excellent too. For example in my above scene I could hide the obvious emissive boards at the windows and still benefit from their output into the GI

Well, that’s my 50 pence for now, really excited to see where the technology goes. Would like to hear if others have any feedback / solutions on my points or what to add more.