Remember the traditional filament bulb? Probably been a while since you’ve seen one. The once-ubiquitous incandescent light bulb, which has remained largely unchanged since Thomas Edison created it more than 130 years ago, has been overtaken by the more efficient LED or the more eco-friendly fluorescent bulb.
How incandescent bulbs work
The traditional bulb heats a thin tungsten wire to temperatures of around 2,700 degrees Celsius but only a tiny amount of the energy it gives out is visible as light, the rest of it is infrared photons which dissipate as heat.
By surrounding the filament with a newly developed photonic crystal structure in the glass, much of the energy that would usually be lost as heat bounces back into the bulb, while still letting the light shine through.
New developments for efficiency
That crystal structure uses nanoengineered mirrors that filter visible energy to allow it to shine through, and reflect the infrared (non-visible) photons back to the filament. The filament reabsorbs them and emits much of them as light, a process the designers call ‘recycling light’.
The old-style bulb was only considered to be 5% efficient, because it typically lost around 95% of its energy to the air as heat. (You’ll have noticed this if you ever tried to unscrew a freshly burnt-out bulb.) LED or fluorescent bulbs boosted that efficiency figure to 14%, but the new incandescent bulb marks a potentially huge leap for energy efficiency to 40%.
Not bad at all. But it could get even better, as the inventors reckon that while this is a good first step, improvements could take efficiency levels still further and that it could even be applied to other industries such as improving the electrical conversion efficiency of solar panels.
Relative running costs for bulbs
The Energy Saving Trust calculates that a 60-watt incandescent lightbulb over a year would typically cost £7.64. An equivalent energy efficient fluorescent or lightbulb drops the cost to £1.53 per year, and an LED £1.27. The new MIT bulb would be expected to cost just 50p to run for a year.
As well as being considerably more energy efficient, the warm, yellowish glow should also render colours much more naturally too. Like traditional bulbs, the new models should have a ‘colour rendering index’ rating of 100, well above the 80 of even ‘warm’ finish LED or fluorescent bulbs.
When can you buy them?
The new bulbs won’t be available anytime soon however. Although the design shows proof of concept, commercial success depends on whether the new crystal structure can be made cheaply enough to make it financially viable. But if that proves to be possible, Edison’s century-old design could be due for a comeback.