Lighting with Emission

Hey folks, so Im working on a project that has alot of emissive surfaces but I end up with alot of noise in the render. Ive seen posts with suggestions on how to fix from years ago but nothing current. Ive tried what was suggested in those posts and it hasnt solved the problem for me. It feels like either Im missing something basic or something is broken

So Ive turned off all the other lights to show the problem (indirect from regular lights is fine, I dont get the noise from them, just from the emissive) So there is one object with emissive texture lighting this area. The sidewalk texture is seamless normally but you can see the seams from each piece and the road is just a plane with a texture so the lightmap is a full square and is set to 1k lightmap. Based on previous posts I changed the lightmass settings as shown. Any ideas whats causing this ? I can get around it by using regular lights but it would be nice if the emissive worked.

you have to place lightmass portals (filed under all Classes) for each light emitting emissive surface. (at least for those contributing substantially to the scene. had the same issue a while back: can't get emissive baked lighting to look acceptable. any suggestions on what I`m doing wrong? - Rendering - Unreal Engine Forums

Ahh thank you, I knew I was missing something ! Much appreciated !

Looking through your post - just to ask the question, Was Unreal able to cope with all the lightmass portals ? Im not using Emission so much inside but I have alot of buildings with exterior emissive features so Im in the same boat as you were, Ill need alot of portals. I guess since its all baked in the end its just a longer build time.

Emissive textures aren’t a good way to do lighting, it’s mostly for effects where you want to notice that something emissive is adding some light to the scene. For what you have there, you can easily use an actual light instead that you just fit to the same size in front of the emissive area.

Well my project is still on 4.19, I havent updated to 4.21 yet so I dont have area lights and I am new to unreal but Ive found it difficult to get away from the very noticeable circular area of effect from spot and point lights in tight spaces. And in order to bounce enough light to get an architectural feel you end up with a bright spot. I know emissive wont cast shadows on moveable objects but Im less concerned about that. The nice thing about emissive is it matches the shape of the object emitting light and gives a nice architectural feel. Plus it just happens automatically rather then having to place actual lights next to every light source. But perhaps Im not doing things right, Im used to lighting in non-realtime renderers :frowning: So my example - the tan image below is a spot light, has a very noticeable circular area on the floor(and bright) but bounces to the other walls well. The blue area is all lit by one emissive plane and has a less distinct, softer hotspot and still bounces very well.

If you’re looking for nice area shapes, and don’t want to spend extra time baking for good emissive quality, I strongly recommend updating to 4.22 for rectangular lights and the new barn door feature. There’s nothing wrong with using emissives for baked lighting, it’s just that you need higher quality bake settings and portals, which can slow down the bake too.

Even with inverse square falloff, the circular/harsh falloff can be visible if your light is super bright. Adjusting the shape can help with the falloff, but regardless it’ll eventually get blown out. You have to find a balance with the intensity and exposure, which physical units can help with that if you’re familiar with those from offline renderers.

Area lights are available in 4.19, it’s just that they’re either spherical or capsule lights

Depending on the type of scene and lighting style, point and spotlights can become pretty useless. and don’t get me started on the hack that is turning point/spots into a capsule light. This has very non-realistic ramifications in regards to shadows and light attenuation (if not static). Your milage and perception may vary depending on the project and or subject matter of course…

Spotlights generally can be broken up a bit by using ies light profiles and very wide outer angles and if you need it broken up even more by using light functions (simulating light obstructed by stuff). Typically I`d say use spotlights only if you really want a light that creates a visible spot ;). Especially in very clean setups these lights can look pretty artificial. The more complex the architecture/ the more detail your scene got, the more forgiving these lights are. For clean environments/flat surfaces the new rectangular lights are definitely a better choice (Especially true when your scene is completely lit with artificial lighting (no windows/sun influence).

Using Emissive and Portals required us to invest in multiple threadrippers to handle even medium quality builds (although GPU Lightmapping seems to come along nicely which could be a remedy).

@rosegoldslugs whats that new Barn Door Feature in 4.22? couldn’t find any info on that…