Editor Lighting doesn´t behave as it should. Decreasing Light is shown as Increasing

Hi There,
Setup the Lighting in a ArchViz interior Scene is tedious since tweeking the Intensity of Lights doesn´t respond well. Decreasing the intensity is shown as increased in editor view. No matter if put the light on static or dynamic(have no Exposure compansation on).
Also some SM objects or Actors whith bright colored textures are shown has black when Backing light maps. As soon as I tweek the Light intnesity, the color comes back untill I bake again.
Is there something wrong with UE4? Or did I put some misleading settings? Is the Graphic Card setting wrong for UE. Thank you