The Return of the Incandescent Light Bulb

Incandescent Light Bulbs

After a recent breakthrough from researchers at the Massachusetts Institute of Technology (MIT), incandescent light bulbs, banned for general-purpose by the Government in 2012, could be making a strong comeback.

Incandescent light bulbs, renowned for their warm yellow glow, were phased out by the Government following an EU directive in favour of more energy-efficient lighting alternatives such as Fluorescent and Light Emitting Diode (LED) lamps.

Why is incandescent lighting so inefficient?

Incandescent light bulbs work by passing an electrical current through a thin tungsten wire (filament). When the electrical current passes through the filament its temperature rises to over 3,000 Kelvin (2,700 °C) causing it to glow with the warm yellow light that we associate with this traditional style lighting. Of the heat that is emitted as light, around just 2% is emitted at visible wavelengths and the rest is wasted as heat (longer infrared (IR) wavelengths). That means 98% of the energy used for lighting an incandescent light bulb is wasted.

Alternative technologies are capable of providing much more energy-efficient lighting, hence the government’s decision to phase out traditional incandescent bulbs:

  • Compact fluorescent lamps (CFLs)
    CFLs are capable of reaching an efficiency between 7 and 13%.
  • LED lamps
    LED lighting is capable of reaching an efficiency of between 5% and 15%.

Incandescent light bulbs have little improved since their invention by Thomas Edison in 1879. However, a team of researchers at MIT have developed a method of “light recycling” that could improve their efficiency to 40%.

How does “light recycling” work?

The research team at MIT have developed nanofilters, made from photonic crystals, that allow the visible light through, but reflect the infrared light. The reflected IR photons are then absorbed by the filament and reemitted as visible light.

In order to absorb as many reflected IR photons as possible the tungsten filament has also been redesigned. The redesigned filament still works the same way as before, only instead of using traditional coiled tungsten wire, thin tungsten ribbon is folded back and forth creating what looks like a tungsten sheet. This creates a larger surface area, making it easier for the filament to absorb more of the reflected photons.

The future of incandescent lighting

So far the team at MIT have managed to achieve 6.6% efficiency from an incandescent light bulb using recycled energy. This is still the low end of the efficiency range from compact fluorescents and LEDs but experts believe they can do better, with the potential to reach efficiencies of 40% – way ahead of alternative lighting technologies today.

However, although this is a step in the right direction, the lifetime of incandescent lightbulbs needs to be addressed. Despite potentially achieving higher energy-efficiency than fluorescent or LED lighting, they can still only last a fraction of the time. Therefore LEDs and Fluorescents are likely to remain the more financially viable option for the foreseeable future.

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