Light still dead after a new bulb?

Start with the bulb you trusted

New bulbs fail out of the box more often than people expect, especially bargain LEDs, and a good bulb can still make no contact if it is not seated. Bayonet caps need a push and a twist until they spring home; screw caps want to be snug, not forced.

The circuit check

Lighting usually runs on its own circuits, often one per floor, protected by a low-rated MCB at the consumer unit. If every light upstairs is out but the sockets work, that MCB has probably tripped, often at the exact moment a bulb blew: the small pop of a failing filament is enough. The reset routine is the same as for any trip: fully off, then back on.

If the breaker drops again as soon as a particular switch is used, stop. A fault in that fitting, switch or cable is doing it, and repeat resets do not negotiate with faults. That is an electrician visit. If the sockets in the room are dead as well, you are in socket territory instead, and the elimination method there applies.

When the bulb was never the problem

Fittings die of age like everything else: lamp holders lose their spring tension, switch contacts wear out, and connections in a ceiling rose loosen after decades of heat cycles. Older downlight setups add a suspect of their own: the little transformer (driver) hiding above each fitting fails far more often than the lamp it powers.

LED retrofits bring quirks too. An LED on an old dimmer may flicker, buzz or refuse to light at low settings, because leading-edge dimmers need more load than an LED draws; the fix is a dimmable bulb paired with a trailing-edge dimmer, which is a switch swap and therefore an electrician job. Persistent flickering has its own guide; sometimes it is a symptom, not a personality.

The dividing line is the same as for sockets: bulbs and breakers are yours, anything wired in is not. The home electrics guide maps the whole boundary.