How many years to change a lightbulb?

For 130 years, inefficient incandescent light bulbs have been the world’s dominant source of lighting. They pass current into a fragile filament that can break at the slightest shock – just the surprise of being switched on can be enough.

Worse, its chief output is heat. Its luminous efficiency (ratio of light output to power input) is at best 2.6 per cent.

Competing technologies have emerged: compact fluorescent (CFL) bulbs, for example, which can offer luminous efficiency of up to 8.8 per cent. But they are relatively expensive, bulkier and slow to turn on fully.

Another is the white Light Emitting Diode. Current LEDs can achieve a luminous efficiency of up to 10 per cent; next generation models offer up to 22 per cent. LED bulbs also boast superior longevity of up to 50,000 hours (equivalent to 17 years with an average eight hours light a day).

For years, LEDs were not bright enough, did not emit the right colors and cost too much, limiting them to traffic lights, a few high-end vehicles, and a range of consumer devices.

But white LEDs are becoming commercially viable. Problems over intensity and color appear resolved and, while they are costly, long life makes them competitive. Long life also allows lighting to be used in awkward places – because with a 17 year life span, there is little need to worry about changing a light bulb.