# (5.6.1) Light function Material stops working when level starts, then remains off when exiting. 

**URL:** <https://forums.unrealengine.com/t/5-6-1-light-function-material-stops-working-when-level-starts-then-remains-off-when-exiting/2717475>\
**Category:** Rendering\
**Tags:** light-function, unreal-engine, lighting-problem, Lighting, question\
**Created:** [April 23, 2026, 2:59pm UTC](https://forums.unrealengine.com/t/5-6-1-light-function-material-stops-working-when-level-starts-then-remains-off-when-exiting/2717475 "2026-04-23T14:59:06Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Celestial\_Scythe](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@Celestial\_Scythe](https://forums.unrealengine.com/u/Celestial_Scythe)\
**Post date:** [April 23, 2026, 2:59pm UTC](https://forums.unrealengine.com/t/5-6-1-light-function-material-stops-working-when-level-starts-then-remains-off-when-exiting/2717475/1 "2026-04-23T14:59:06Z")

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So I have a scene that has a light function material to create a flickering light effect. I use the same material for the emission on the object. When I first open the project, I can see the effect and it seems to function correctly.

However when I “Play this level in active level editor viewport”, the Light Function Material stops working. I can see the flickering on the emission itself, but the one attached to the RectLight is clearly no longer working.

When I exit the “play in viewport”, the Light Function Material remains off and I have to close Unreal and re-open to get it to work again.

The Light is set to Stationary, Lumen is on, Support PointLight WholeSceneShadows is checked on.

I’m hoping that someone here might have a idea of what to try, as I’m fresh out.