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Illuminating dark corners. Multiple skylights?

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Kligan polycounter lvl 4
I am facing a bit of a conundrum here.
To illuminate my indoor scene I'm using Stationary Directional Light with indirect lighting intensity of 40, and Static Sky Light with indirect lighting intensity of 2 that captures an HDR cubemap . The light comes through windows and illuminates the room with light bounces from walls and other surfaces. The Skylight in this case is used specifically to give an additional illuminated area around the points where Directional Light hits the surfaces.

However, that leaves me with some dark corners in places where light bounces do not reach.

My first thought was to just slap an additional Skylight with 0,05 intensity into the sceme, set it to Movable, disable shadows and call it a day. It does exactly what I needed - no more pitch black corners.
However, as you've might guessed, the engine does not like that, and gives me an error after light building. 

Is there any way to go around this issue? 

What I'm doing so far is building the light with Static Sky Light, then disable it (the lighting information remains because it was built), and enable the Movable Sky Light. But that does not feel like a proper solution. 

Replies

  • Obscura
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    Obscura grand marshal polycounter
    How about allowing the lights to bounce more? This does not really increase the build time.
  • Kligan
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    Kligan polycounter lvl 4
    I have 25 bounces in the World Settings.
    Increasing it further does not really give much of a result. And increasing the Indirect Lighting Intensity on the Static Sky Light illuminates already lit areas further, while leaving dark corners intact.
  • Obscura
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    Obscura grand marshal polycounter
    I'm lot a lighter pro but to be honest, if you need to set the indirect illumination intensity to 40, you are probably doing something wrong.

    Can it be an exposure problem? Maybe?
  • Kligan
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    Kligan polycounter lvl 4
    No, I have my exposure set to neutral so far. I'm just setting up the lighting on a test scene before proceeding to the actual scene.
    The idea with 40 indirect intensity is to illuminate the area with ambient light from directional light. I was trying to experiment with creating natural lighting environment as opposed to faking it by adding global illumination via sky light.
    I watched some archviz videos on youtube, curious about how they achieve such high lighting quality in ue4. And I discovered that they are using high values on indirect lighting. And it actually works, but takes some experimentation to adjust correctly. 

    Here's this video, for example: 
  • Obscura
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    Obscura grand marshal polycounter
    That might be the problem. To get bright interiors, exposure needs to be changed. It works kinda like your eye. When you are looking in on a window of a building, the inside appears dark until your eyes gets used to it. When you are inside, the outside looks blown out. This is how it works in Unreal too. So try playing with that, and don't get scared if the exterior gets blown out. Its normal. It happens in real life too.

    Also, do you have a background sky sphere in the scene or something? Its important to have it because it takes a big part of the lighting. The skylight uses that. Unless you manually give it some cubemap. If you have black background and np cubemap either, reflections and lighting will always look off and dark.
  • Kligan
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    Kligan polycounter lvl 4
    Yes, I do have a custom sky sphere blueprint setup to use with HDR texture.
    I don't want to touch the exposure until the very end, to adjust the final look of the scene alongside with other tweaks like color grading and other effects.
    The reason I work with neutral exposure is to make sure no lights are blown out of proportions. And I'm trying to use real life light values as well (like candle being 12,7 lumens).

    My testing scene looks like this so far (medium lighting build quality):
    https://i.imgur.com/MKpJOKr.png

    Overall it's not bad, and it will be brighter in the actual scene because there will be windows in the brick walls, and candles, and chandeliers, and a fireplace.
    I was just wondering how to tackle illuminating dark corners when using light bouncing approach. So far, as I said, I ended up with two sky lights - one for baking lighting, and the other one to enable it after light baking to illuminate dark corners.
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