How to use DMX Modulators to create a global dimmer channel that will effect the dimmer of each cell in a matrix proportionally. This tutorial assumes you already know the basics of DMX and you are trying to extend what you can do with the built in DMX fixture examples provided in Unreal.
https://dev.epicgames.com/community/learning/tutorials/daa9/unreal-engine-dmx-modulators-creating-a-global-dimmer-for-matrix-fixtures