Basic lighting question

I know this is probably a simple question but it’s driving me nuts. Lighting has always been something I’ve not really understood properly even though I’ve been creating games for a couple of years.
In the two pics attached I have a simple room with a nice wall and floor - temporary roof. I have set the walls to static - the floor is still a box geometry as I’ve not finished chopping it about.
I have also set the light to static and it looks fine. But when I build the lighting the roof and wall go dark.
If I set the wall to stationary it works ok but then performance starts to suffer if I have a lot of objects.

The third pic is to give an idea of the complexity of what I’m building so getting the light right is pretty important!

So what combination should I be using do give me the lighting I want with best performance? And am I missing something obvious?