By Sarah Knapton, science editor
An incandescent light bulb
Ever since the EU restricted sales of traditional incandescent light bulbs, homeowners have complained about the shortcomings of their energy-efficient replacements.
The clinical white beam of LEDs and frustrating time-delay of ‘green’ lighting has left many hankering after the instant, bright warm glow of traditional filament bulbs.
But now scientists in the US believe they have come up with a solution which could see a reprieve for incandescent bulbs.
"The lighting potential of this technology is exciting."
Prof Gang Chen, MIT
Researchers at MIT have shown that by surrounding the filament with a special crystal structure in the glass they can bounce back the energy which is usually lost in heat, while still allowing the light through.
They refer to the technique as ‘recycling light’ because the energy which would usually escape into the air is redirected back to the filament where it can create new light.
"It recycles the energy that would otherwise be wasted," said Professor Marin Soljacic.
An energy efficient light bulb
Usually traditional light bulbs are only about five per cent efficient, with 95 per cent of the energy being lost to the atmosphere. In comparison LED or florescent bulbs manage around 14 per cent efficiency. But the scientists believe that the new bulb could reach efficiency levels of 40 per cent.
And it shows colours far more naturally than modern energy-efficient bulbs. Traditional incandescent bulbs have a ‘colour rendering index’ rating of 100, because they match the hue of objects seen in natural daylight. However even ‘warm’ finish LED or florescent bulbs can only manage an index rating of 80 and most are far less.
"This experimental device is a proof-of-concept, at the low end of performance that could be ultimately achieved by this approach," said principal research scientist Ivan Celanovic.
"An important feature is that our demonstrated device achieves near-ideal rendering of colours".
“That is precisely the reason why incandescent lights remained dominant for so long: their warm light has remained preferable to drab fluorescent lighting for decades.”
Thomas Edison patented the first commercially viable incandescent light bulb more than 130 years ago so that "none but the extravagant" would ever "burn tallow candles.”
It works by heating a thin tungsten wire to temperatures of around 2,700 degrees Celsius. That hot wire emits what is known as black body radiation, a very broad spectrum of light that provides a warm look and a faithful rendering of all colours in a scene.
The first prototype CREDIT: MIT
However most of the energy is wasted as heat which is why many countries have now phased out the inefficient technology. The UK government announced in 2007 that incandescent bulbs would be phased out by 2011 however many manufacturers still sell them, using a loophole which says they can be put in industrial buildings.
The Energy Saving Trust calculates that typical living room usage of a 60-watt incandescent lightbulb over a year would cost £7.64. Using an equivalent energy efficient fluorescent or ‘CFL’ lightbulb would cost £1.53 per year, while an LED would cost just £1.27.
But if the new bulbs live up to expectations they would cost under 50p a year to run and even improve health.
Previously researchers have warned that the blue light emitted by modern bulbs could be stopping people from getting to sleep at night and campaigners have expressed concerns about the dangerous chemicals they contain.
Prof Gang Chen, Head of the Department of Mechanical Engineering at MIT added:
"The lighting potential of this technology is exciting.”
The research was published in the journal Nature Nanotechnology.