Why does a lightbulb get suddenly much brighter shortly before it blows?
In: Physics
Two possibilities:
If it blows when first turned on, which light bulbs often do, the filament is cold. When the filament is cold it’s resistance is lower, that means, as per Ohm’s law (Current equals Voltage divided by Resistance), the current flow will be much higher and it vaporises the filament almost instantly.
That will result in a much brighter flash than you’d expect from the brightness the bulb normally outputs.
If it blows when it’s hot, the filament fails, and there’ll be an electrical arc can be formed between the ends of the filament. This electric arc will be much brighter than the light from the filament, and as the ends burn away the arc will widen getting brighter. Arcs behave in the way that as they get hotter, their resistance falls, so again the output will get brighter and brighter until the filament burns away or the breaker trips. All this happens in an instant, in both cases, so it just appears like a super bright flash before the light disappears.
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