By Jonathan Duffy BBC News Magazine

The days of the humble light bulb are numbered, with plans to phase it out by 2011 in favour of energy-saving bulbs. Before consigning it to the dustbin, it's worth reflecting on how this cheap and disposable piece of technology has changed the world.

Asked to reflect on the recent backlash against Thomas Edison's pioneering "invention", his great-great-grand nephew strikes a positive note: "It's served us well for over 100 years", says Robert KL Wheeler.

But as the inverted commas suggest, this is not the first time the humble light bulb has been fought over.

Its very inception is a long-standing point of dispute among historians and engineers, with many, especially on this side of the Atlantic, crediting it to a Brit - Sir Joseph Swan.

Judging by Chancellor Gordon Brown's pronouncement this week to phase out these energy-sapping bulbs within four years, the debate seems destined to outlive the invention itself. Australia and California have already announced plans for a ban.

Yet in discarding the unassuming old light bulb, it would be reckless to overlook its impact. For a spurned piece of "obsolete" technology, it still shifts by the truck load - some 200 million a year are sold in the UK. It's hard to think of another electrical component that is more affordable, ubiquitous and disposable; its influence more profound, than the familiar incandescent tungsten filament light bulb.

Let there be light

Sure, it's about as environmentally sound as a Humvee with an oil leak, but then the bulb that millions of us flick on and off several times a day without so much as a second thought, is largely unchanged from the one that Edison patented 127 years ago.

HOW THE LIGHT BULB WORKS Bulb filled with inert gas Current heats filament to very high temperature Filament becomes excited, releasing thermally equilibrated photons in the process

The light bulb, says Brian Bowers, former curator of electric engineering at the Science Museum, ushered in the electrical age in the home.

"The light bulb grew up with the electricity supply," he says, noting that in the 1880s, just after the bulb was invented, there were only a few, isolated power stations in Britain.

"It gave a purpose to electricity. It was what brought it along."

Artificial light pre-dates Swan and Edison's eureka moments. Candle light, oil lamps and, by the 1820s, gas lighting helped extend the day beyond the setting sun. But these were dirty, messy and smelly ways of illuminating a room, and, before gas, the light itself would be little more than a dull glow.

By the mid-19th Century, the light bulb had been solved in theory - all that was lacking was the technology to make it work. Several inventors were on the case but it was Sir Joseph Swan who figured out how to create a vacuum in the bulb - thereby starving the filament of oxygen so it would glow slowly, rather than burn out in a flash.

Edison originals: Two bulbs up for auction in 2006

Edison, meanwhile, cracked the carbonised filament, says Ian Peterson, of the Museum of Electricity, and set about making it marketable.

A glance at the diagram filed with his initial patent in 1880 (see below) shows how little Edison's light bulb has changed.

After thousands of years of man living by the natural rhythms of the sun, suddenly a room could be lit up with the flick of a switch. But with few houses actually wired up, the electricity industry used lighting to sell its benefits.

"Electricity sold itself on its cleanliness and simplicity, and also associated itself with modernity," says Frank James, professor of history at the Royal Institution.

At the same time, engineers were busy refining the light bulb, discovering tungsten glowed brightest. The final refinement came in 1934, with the inter-twining of two filaments to make a brighter lamp and a longer-lasting filament, says Mr Peterson.

"When you buy a light bulb today, you are buying precisely 70-year-old technology," he says.

Cover of darkness

At about the same time, the National Grid came online and by the end of the 1930s, half the households in Britain had electricity. Twenty years later, it was nearing 100%.

When you buy a light bulb today, you are buying 70-year-old technology Ian Peterson

Today, no one pays a second thought to electric lighting, at least in the West. Our ability to banish darkness at the flick of a switch has upturned our lives, says Professor Roger Ekirch.

"It has transformed nearly a half of every day in terms of how we divide our time," says Prof Ekirch, author of At Day's Close: A History of Night-time. Before artificial light, night time was a time of "real and imagined fear".

The near-absolute anonymity of darkness accommodated horrific violence, says Prof Ekirch, as policing was largely impossible. The murder rate was five to 10 times higher in Britain, than today. Darkness was also the attendant of superstition and it's no coincidence that the intellectual enlightenment of the 19th Century accompanied the more tangible enlightenment.

But while "pre-industrial populations had thousands of years to adjust to nocturnal darkness," says Prof Ekirch, the light bulb has interfered with, perhaps even corrupted, the 24-hour circadian rhythm of our body clocks.

Edison's patented bulb, left, from 1880, and a more modern incarnation