Spot and Point light leaks - any advice?

Hey folks, doing some procedural generation with 3D tiles, so can't bake lights. Basically left using Basic Realtime Lighting:

However, I'm having a little trouble as I'm finding point and spot lights shining 'through' seams of my test modules... (see the little white bar of light at the back of the first four modules)

(The rightmost module has no backfaces - I clearly need to include those backfaces in order to occlude the majority of inappropriate light).

Can anybody advise me if there's a way to 100% exclude light leaks like these, or if I just need to be super careful about where I place the light objects?

I'd love to get some kind of authoritative verdict on this! Many thanks in advance!