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4.19 Physical Lights

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    Hello everyone. I have been following this thread for a while, and I have been trying to figure out physically based lighting in UE4. I have come up with a tool set and workflow, that so far works for me. Check out this tutorial I made, tools are in the description.


      Sorry to bring back this thread from the dead, although I have to say, it was really interesting from the first page.
      The thing is, I'm finding a large discrepancy between what I get in Unreal and what I'd expect, but I'm not an expert on the field so I want to be sure that I'm not the one doing something wrong.
      I'm working on an archviz scene and I'm testing physical light values, but while I'm getting a good looking result with sun and sky lights, artificial lights seem off.

      I've got a completely dark scene, except for a point light at 800 lm, at 1mt from both walls and 1.80mt from the floor. The camera settings in the PPV are 1/60 for the shutter speed, 100 ISO, 2.0 f-stop, so around EV 8. As you can see by the screenshot the room appears very dark and the light is barely visible. I can't understand if this result is correct or not, but from the tests I made with my phone's camera with exposure settings set to manual, it's very dark compared to real life. The second screen shows the base color, and you can see my textures are not too dark. Can anyone help me understand if there's still something wrong with Unreal, or if this behaviour is expected? To me it looks like the issue that Daedalus51 had with 4.19, when a good eye-balled value was around 10x the expected lumens value.
      Also, I've disabled every PP effect that might add shadows/influence lighting.

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      Filippo Romani CG Artist


        Originally posted by Kel Solaar View Post

        For future reference, we spent a few hours digging and found out where the 1.2 value is coming from: It is actually normative as per ISO12232:2006, i.e. an ISO Standard derived value, referenced in Wikipedia, in Moving Frostbite to Physically Based Rendering 3.0 (and confirmed by that bit of maths in Unity code):

        1. // Compute the maximum luminance possible with H_sbs sensitivity
        2. // maxLum = 78 / ( S * q ) * N^2 / t
        3. // = 78 / ( S * q ) * 2^ EV_100
        4. // = 78 / (100 * 0.65) * 2^ EV_100
        5. // = 1.2 * 2^ EV
        6. // Reference:


        So Epic has just documented that whole thing properly which is great:




          sorry for necromancing this thread but I still fail to understand the new physical lighting workflow. Let's say I set up lighting in my scene according to real photometric values, so that during sunny day noon, the sun intensity is around 111 000 lux and indirect sky intensity around 20 000 lux. If I use real world camera settings, such as f/16, ISO 200 and 1/125 shutter, I get more or less what I'd expect.


          look development of emissive materials becomes borderline impossible. Even if I set preview scene settings in the material editor to match the exposure range, thumbnails of the emissive materials with emissive values large enough to be visible under EV100 daylight setup are pitch white in the content browser:
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          It seems that the physical lighting scale was somehow hacked into the engine, but when I try to actually use it, I encounter quite a few engine areas which just aren't built to handle that...


            I had the same concern and experienced the same issue. I had an interior scene that I re-worked with light values and settings based on this thread. All good until I noticed there are fx elements with emissive textures that are not compatible.