Depends on the length of each track. Let's say you have 8'-0" track sections. You would need six, two for each long side of the layout and one for each short or 7'-0" side of the layout. I would guess that four lighting heads should be sufficient for each track section. So you would need 24 lighting heads. Since they will be dimmable, you can't have too many. But 24 should be fine.