how to add ambient light in a closed space.

I am trying to light a room that is contained in a box. I want to introduce an ambient light. My question is. Is the skylight the best light to use so I can introduce a bit of ambient?
If its true that the skylight is the right tool to use to introduce ambient then how can I make ambient light appear in a closed box?

If you will use skylight it will cover all the map, instead use post process volume with ambient cubemap

I think you need to re-evaluate your environmental design of the room and somehow accommodate a light that lights it up instead of relying on an ambient light.

I really miss the kind of omni light feature we had back in UEd3. it does not require cubemaps/sky to get its brightness and colour from like the skylight we have in UE4. you could set a (minimum) brightness and colour, wich really helps a lot not only in the above indoor situation but also in many others where you dont need realistic lightning, but just general brightness to see stuff.