Download

[4.27-5.0EA] Casting dynamic light from emissive material?

Hello there!
Sorry for the the rather dumb question but I am not very up-to-date with the current lighting technology standard. I’ve now read multiple times about it, but the threads were all so old, I wanted to recap it.

Is it possible to dynamically light objects using emissive materials only?

According to this document page here, it is only available for baked / static lighting and therefore also does not light characters:

Which makes it rather impossible to heavily use in level design. It would affect the pre-baked world lighting and not the character and to correct this lack in detail, one would have to fake it with standard lights. Then most of the advantages are gone too. How do you deal with that?

Do you think dynamic emissive materials will become reality anytime soon?

EDIT: Did I not hear about this in UE5 talks. Does Lumen support dynamic emissive materials? Do you need RTX hardware for this?

In UE5 with Lumen, yes, but the results won’t be very good unless your emissive lightsource is large and dim. Lumen does not require hardware raytracing to get this effect.

In UE4 you’re limited to baked emissive. Unless you use RTXGI.

Characters can receive baked/static emissive light just fine, it is baked into the volumetric lightmap which is used to light skeletal and dynamic meshes.

Skeletal/dynamic meshes can’t emit emissive light onto other actors in the scene. Depending on what you’re doing though you can often get around this by simply attaching lights to an object/character.

2 Likes

In what way would the results be “not very good”, I’ve only seen a few videos and it didn’t seem bad quality-wise.

So characters are able to receive emissive light? I just read in the docs page, so I wouldn’t know.

Thank you very much for your response. I’ll keep looking : )

It won’t be visually stable, you’ll get noise that looks like soft glowing spots and depending on how small the lightsource is, it may not emit any light at all when off screen.

Daniel Wright gave an explanation of this in his livestream presentation

Yes characters can receive emissive light. The docs page is correct. Emissive light is static (in UE4), the actors that receive it can still be dynamic.

Conclusion […] However keep in mind that when using Emissive Lighting the Emissive Lighting will not illuminate dynamic objects, like characters, the same way that lights will. […]

Alright, I just read it again and might’ve just overread the “the same way that lights will” part. Guess I just understood it as it doesn’t illuminate them at all.

Yeah, I stumbled upon Working emissive materials in RTGI (with screenshots) even before starting this thread but couldn’t make much of it. I guess the denoiser problems mentioned ended up still being a general issue.

Thanks for your help!

Well… I can understand why you read the documentation that way, 'cause I’m reading it that way too. Guess I should have checked before I said “it’s correct”. It still might be but that’s some confusing phrasing for sure.

Regardless, if you still have any doubt I can demonstrate that it works:

Flying cubes are moveable meshes, first person arms/gun are skeletal meshes. The cubes are also casting dynamic shadows from the static light through indirect distance field shadows. Skeletal meshes can do similar via capsule shadows but that’s not shown here.

1 Like

I see, then at least I’m not the only one confused by the phrasing : D

Thanks for taking the time!