I have a completely new scene in UE4.25 and when I change the Intencity of my DirectionalLight I don’t see any effect. It is exactly the same when it’s 10 lux and 1 lux:
That’s probably the exposure in the editor adjusting to the light. In the viewport under the “lit” tab, at the bottom find Exposure and untick “game setting” that way it’s using the “fixed” setting below. I hope that works