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SoftDice

Lighting with G.I in physical render

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Hey people.

I have this LEGO scene with some small lego huts that have glass windows, that i'm trying to render.
I have a sunlight, two other lights to light up the shadows and then a light in each of the huts, so you'll be able to see inside when the animation is rolling.
When i render with Global illumination, everything looks super nice, except for the windows. You can see through them, but the room is not illuminated at all, i can see through one window and out through the one behind it, but the room is pitch black.
What am i doing wrong? I remember reading something about global illumination portals, but i can't seem to figure it out. 
I hope someone can help me out, if you need more information just let me know and i'll post some pictures.
Thanks and have a nice day everybody!

Screenshot 2019-05-27 at 16.43.52.png

Screenshot 2019-05-27 at 16.43.58.png

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First thing to check is that your glass has been modelled with real world thickness... if it hasn't you can't expect light to pass through it properly...

Next thing to check is only applicable if you are using Ambient Occlusion, and if you are, you must have 'Evaluate transparency' ticked there.

Likewise in the Physical Render make sure you have the Shading Transparency Check ticked also.

 

Then it just comes down to your material settings, which should be a colour channel set to black with 1-3% brightness, and a transparency channel set to 99% Brightness, and with a Refraction index of 1.55, Exit Reflections turned off, and no other channels at all, except possibly Reflectance, which should be a single layer beckman with a dielectric fresnel and about 20% global strength.

 

CBR

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^^eveything that he said.

 

Also - look at the phong angle of your glass objects.  If they are just Cubes of glass (as they should be) - then you can remove the phong tag.  Sometimes having phong on straight glass can mess it up.  Glass should be about .63cm thick.

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evanalexander.com     Abusing chromatic aberration heavily since 2011....

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Another thing I'd probably do is kill off specular in any reflectance layer. Even though you have regular lights in your scene generating that, and technically all surfaces do feature a specular component, it'll be a nicer result if you just turn that off, and instead pick various lights to 'show in reflection' (details tab of each light). Note lights will have to be Area type for that to work, but to be honest you should be using those anyway, with Area Shadows for most realistic results...

 

CBR

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  • Topic Author
  • Thank you @Cerbera and @EAlexander !
    I'll try it all out when i get to work!
    And now when i think about it, it's actually not glass, it's a transparent lego brick, would you approach it another way then?
    On the package, the window/transparent brick, is somewhat diffused with white, like maybe 10%, how would i achieve that?
    Thanks again guys!

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    Just now, SoftDice said:

    On the package, the window/transparent brick, is somewhat diffused with white, like maybe 10%, how would i achieve that?

    You can just turn up Transparency blur a little to get that effect. Does affect render times (makes them longer), but they're not too big in the scene so that should be OK.

     

    CBR

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