As Lucian has explained, you have two requirements for protection:
- Fault protection (eg. short)
- Overload protection (e.g. too much plugged in to on a set of sockets)
Usually you must have fault protection (with only a few special exceptions), however, overload protection is not explicitly required for
fixed loads.
Here the MCB is only providing fault protection, so as long as the MCB's disconnection time is acceptable and the let-through energy (i.e. the I2t) is below the cable's adiabatic limit for not damaging the insulation for an infrequent event, all is OK.
Overload protection is not normally needed on a
per-light basis, as Lucian explained. Thankfully we no longer have those adaptors to allow appliances to be plugged in to a bayonet socket!
However, for anything with multiple load points that can be plugged in you would normally need overload protection, so the light circuit MCB ought to be coordinated with the main cable(s) feeding the lights, just as you would for the MCB protecting socket outlets. But smaller, obviously!