Hi unreal community !
I need help with shadows and lights. I’m creating a black and white only game with no shadows. I’d like to have an area (a cave) all black with some " lights " that would reveal the white parts of environment.
Any idea how can I do that ? Do I need to set up lights ? Or a post process thing ?
I can’t find tutorial about this specific case 
There is nothing specific. Just create level without lights and place light sources where white spots should be.
Like Redbox said, you could just create a level without lights place and place the lightsources where-ever you need your lights to be. However, if I am understanding your question correctly, you ONLY want the colors black and white, not any grey values. If that’s the case, you will also need to have a post processing material, something like the setup in this picture (though I got better results with the 0.05 value set to 0.1 instead):
Of course, this turns everything into either 1 or 0, meaning all anti-aliasing is gone. If you still want to have anti aliasing as well, you will probably have to work with SphereMasks rather than lights. This setup will be much more annoying (since it would take a lot of juggling with spheremasks and dynamic parameters on the materials).
Thanks a lot for your help 
you are awesome guys