Three different things here.
When you're building an airport and you intend to have a min RVR <400 you should install runway centreline lights.
On the day, the centreline lights are inop, or you are flying outside the EASA region at an airport with none. You require 300RVR for takeoff.
If the first section RVR is inop, then you can count the visible lights to assess the RVR yourself for the first section only.
Hope that helps!