Overview
This simple solution for those who have old PC (pre DX10 GPU) or those who have gamma issues with game. If you can launch the game but scene too dim/dark try this solution.
Before/After
Before:
After:
Solution
1. Goto:
C:Users<YourUser>AppDataLocalRSGSavedConfigWindowsNoEditor
2. Edit:
Engine.ini
3. Add section:
[/script/engine.engine]
DisplayGamma=5
Save file and launch the game. Enjoy.
PS: I prefer lower gamma value, like 4 or 3.5. 5 is too bright IMO.