Is there a way to fake shadows and reverse the light?

Development Rendering
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1

i have two questions here,

  1. is there a way to make a light only cast object’s shadows and not influence the lighting? in the other words, the light doesn’t light up objects but only fake the shadow.

  2. is there a way to reverse the light intensity and make it a negative number? instead of making light, it absorbs a part of other lights that i don’t need.

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because I know in some other 3D software, they can do it.

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  1. Yup. Open actor details and in Lighting tab you can find little arrow. Click and then toggle “Hidden shadows”. From now on object will cast shadow even if it is not visible
  2. Hm, it was possible before. Seems like Epic removed this option :frowning: In earlier versions you could choose Light color you want and then change intensity to negative value. This way you “remove” from objects light color you’ve chosen. I even used it in some old projects
4

thank you ~ bro ~

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Hey zeOrb,

Thank you for your answers first, but for my first question, I want to know how to make lights that only cast objects’ shadow instead of lighting objects.
Do you know how to do that ?

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Well it is still possible to have negative light intensity, though it can create visual artifacts: [Request]:Negative Lights - Rendering - Epic Developer Community Forums

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King of cheap hacks here, at your disposal!

Instead of using negative intensity, change shadow filter bias to a negative number. This will invert the shadowing on your light sources, which is better than negative intensity as it doesn’t actively bork colours :slight_smile:

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Hey Amber,

I tried your idea. but when i set the shadow bias to a negative number, the shadow just disappear.
Instead, If I set the shadow filter sharpen number to negative, the shadow becomes a lighten shadow.

and btw, how to set up this ( [Request]:Negative Lights - Rendering - Epic Developer Community Forums ) in a correct way. It seems like that it doesn’t work for me or I didn’t set it up in a correct way.

would anyone explain it to me with more details please? Thank you !

9

Do you want negative lights, or inverted shadowing? The two are not the same thing - lighting and shadowing are two different systems.

Inverting shadows works like I mentioned, by supplying a negative shadow filter sharpen, you’ll invert the placement of shadows, creating light where shadows should be and vice-versa. If you want a negative light, give it negative brightness at run time and it will remove light from the scene - the link you’ve supplied should do exactly that, I’ve tested it just now and it works as expected.

Be aware that negative lights will still cast normal shadows, and may well cause rendering artefacts.

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Hey Amber,

I want negative lights. but I cant find that Set Bridgtness Node…

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It’s ‘Set Intensity’.

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Does the output of the Set Intensity Node have to link to something?

because right now no matter how large the negative number I set , it still doesn’t have have effects.

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thank you ~ ^.^ Amber ~

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You’ll see it in the editor only when you run the preview (e.g. by clicking ‘simulate’).

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Thank you very much, dear Amber ~

it works now ~

16

Looks like this don’t work anymore in new versions, is there some other way ?

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I’m also interested in negative light. Because of the quite strong use of Skylight my underground part of the level (which does not contain any light) is incredibly bright.

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Thank you, Good

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Was anyone able to achieve this negative lighting in newer versions? It just wont let you use negative values it only goes to 0