All incandescent light bulbs use a tungsten filament. When the filament
fails, this is because it eventually melted away to be an opened circuit.
Over the lifetime of a light bulb, as the filament is heated to near white
hot temperatures to generate light, it starts to slowly break down.

When the filament in a lamp burns out, it sometimes has a bit of a meltdown.
Sometimes pieces of it can short out the metal support contacts feeding
itself. If there is a short, it can cause a fuse to blow, or a circuit
breaker to go to the open mode.

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JANA
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"hooch" wrote in message
...
I have two halogen bulbs on the same lighting circuit (240V - UK)
controlled by the same two switches, i.e, either switch will turn on
or turn off both lights. Recently one of the two bulbs died (open
circuit, as expected), causing the fuse / circuit breaker to trip.
Can anyone offer an explanation?