Static light misbehaving

This problem has plagued me for a long time and I’ve finally reduced as many variables as possible to try to find the cause.

Static lights are changing their behavior in my level. In the following examples, I have disabled all lights except a group of blueprints of the same class, which contains a spot light pointing at the floor. I have disabled GI, AO, and all SphereReflecttionCaptures. The Post-Process Volume has also been disabled.

Below is a video, created using Matinee. You can see the light change toward the end of the clip. It is most noticeable in the tables in the foreground and on a broom to the left of the bar, in the background

Below are two images also illustrating the problem. The first image was taken when the editor was idling. The second image was taken 4 seconds into simulating the level. The camera never moves and the simulation remained like the first image, but then switched to the darker one. When i stop the simulation, it reverts to the first image.

If someone can tell me why this is happening or how to resolve it, you’ll be my hero.

Hey SteringY,

If you change your lights to stationary or static does the light disappearing still happen? I am curious to see if this is an issue with the light mass or the lights themselves.

If they are still flickering then this could be a culling issue.

Blueprint components, often times, can be set to inherit the bounds of their parent, which can cause issues if the parent has smaller bounds than the child. I will link you to documentation that will elaborate further:

There are several work arounds :

1.Disable all occlusion culling for your screen by going to Project settings > Rendering > Occlusion culling and checking the box off.a.) Since you are wanting this utilized on static meshes this may not be the best option.

2.In the viewport under Show > Visualize > Out of bounds pixels. Check this on and then enter the command r.VisualizeOccludedPrimitives 1 to see, in your scene what is being occluded behind what your looking at.

3.The last option, is there is a console command r.hzbocclusion 1. This defines which occlusion is being used. This will allow for a more accurate calculation of your bounds.

More specifically in your meshes if the parent is exceeding the area of the bounding box then then the parts of the mesh will disappear or remain on the screen after the bounding box moves completely off camera.


Thanks for the suggestions.

Currently, most lights are off because I wanted to reduce the number of variables that could be causing the problem. The lights that are on, are all set to static, When I set them to Stationary, I do get the flickering, but some lights become movable because of too many lights overlapping. If I set them all to movable, the problem continues.

My thought was that Static lights would simply cook and everything would be fixed and I wouldn’t have to worry about anything.

I set everything you suggested in steps 1-3, but don’t see anything out of the ordinary except occasionally on the hands of one of my characters ad he moves them through light:

Sorry it;s so dark

As for bounding boxes, I increased the scale size. but it doesn’t seem to have an affect.


I had someone else download the project and run it on their machine. They didn’t see the problems I have, so I migrated the level to a new project, from 4.9 to 4.10. Amazingly, the problems seem to have gone away for me as well. Unfortunately, I can only test this with the lights set to Movable because I can not build lighting with the lights set to static due to the swarm agent not launching. I believe this has to do with the Substance plugin.

UPDATE: I still have a major problem. I now have the level migrated to another blank 4.9 project, which is not on my Google Drive (I thought that might have been an issue) and everything was going well, but suddenly, lights turned off. This can happen or not happen, and at any time during playback or while NOT playing. There doesn’t seem to be anything consistent that I can point to . Unlike before, I have a mix of Static, Stationary, and Movable lights.

You can see a new video here: - YouTube

In it, you will see lights flashing on and off, but when I PLAY, some lights just switch off.