It seems like the lighting quality and accuracy heavily drops when I go to build my lighting on production quality (or any quality for that matter… the only lighting that actually looks good is the preview.
For instance here is the preview lighting.
and here is the production quality lighting.
suddenly after building the lighting the light leaks through the top of the the “lighthood” even though the lighthood is placed firmly against the wall (partially going through the wall).
and here is what it looks like when I replace the point light with a static mesh of a flourescent light with an emissive material.
notice that directly under the light there is no light being rendered and on the wall next to it I get a nasty square blotch that looks terrible… Then on the ground there are blotchy circles of light and shadow that make no sense at all. Any help would be appreciated.
Hi VictorVaeVictis,
There is a difference in the quality of lighting when using Preview vs Production. This difference is changing the number of indirect lighting bounces and other lightmass settings to give you a “preview” of what the lighting will look like. It will inherently be inferior to building lighting with Production. There tends to be more light leaks and less accurate shadows. Think of this like the Engine Scalability settings except for Light Builds with Lightmass.
In your first image This looks like you’ve already built the lighting on the Preview level possibly. The error here is that it looks like your light is sitting partially in the wall causing part of the mesh to project a shadow inside that should not. You would need to move the light outward more so that it’s not penetrating the wall in such a way. If you’re wanting to use something similar to a fluorescent light try adjusting the Source Radius and the Source Length of the point light into the shape of a tube light.
In the production build it’s some of the same things as mentioned above. A lot here can also be determined by your UV layout and how light is being handled on the surface of an object. This leads directly into Lightmap resolutions playing a large part of you static lighting quality as well.
Here are some examples I’ve setup to hopefully demonstrate some of this for you.
Lightmap UV Layout
Lightmap resolution set to 128 unless specified otherwise
Preview Light Build:
Production Light Build:
If you’ll notice there is still some bleed that is coming from the light that is affecting the front of our light housing above the door.
If you adjust the Indirect Lighting Intensity and change this to a value of 0 so that there is no GI contribution or even a very low value you can get better results that give a more natural look.
Indirect Lighting Intensity 1 (Default)
Indirect Lighting Quality 0
Emissive Lighting used as static lighting bakes the lighting directly into the lightmap. So this can directly affect the object where lighting is baked if the light map resolution is not high enough and if there is not a good UV layout for the lighting to be baked at a decent quality.
Emissive Lighting:
LM Resolution 64
LM Resolution 256
LM Resolution 1024
As you’ll notice the smoothness of the emissive lighitng increases with the lightmap resolution. While this may produce better results it also means that more texture memory is being used. This is not an ideal use case for emissive lighting as static lighting necessarily. You also don’t have control directly over how the light is baked as you do with static lighting.
Please take a look at our Wiki Lighting Guide for more common lighting issues as well: A new, community-hosted Unreal Engine Wiki - Announcements - Epic Developer Community Forums
I hope this has been helpful. 
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Thanks for the reply Tim. I tried pulling the light further away from the wall but it didn’t seem to make a difference… even at absurd distances the light still leaked through the hood. I also tried increasing the lightmap resolution of both the wall and the ground and that helped a small amount but not enough to justify the memory usage. That does help me narrow it down however. Now i’m starting to think it may be a problem with my UV map not being set up properly… I’ll play around with it for a while and see what I get.
If you need here is the asset I used in the test images above: Dropbox - Error
Maybe that will help if needed. When you import, let UE4 generate the lightmap UV. I didn’t create a custom one in 3Ds Max when I made it since it’s a simple object.
To get better lightmap resolution, it’s probably would be best if your mesh is broken up into several smaller pieces (if they are not already) and snapped together like lego building blocks.
Feel free to post your progress or any questions here and I’ll help out when I can. The community is also really well versed in some of these areas and have solutions that could help as well.
