Recent developments have produced an incandescent lamp with an efficiency approaching that of CFLs, but without the associated problems.
Incandescent lamps have been largely replaced by compact fluorescent lamps (CFLs) and LEDs, mostly because of the low efficiency of conversion of electrical energy to light. The latter two technologies use approximately 30% of the energy used by incandescent lamps for the same light output.
Although CFL and LED offer energy savings, they come at a higher price, have internal electronics, and are limited in terms of colour spectrum and dimming controls. LEDs are becoming more and more popular for commercial applications but are still expensive for residential and small installations.
Researchers have warned that the blue light emitted by modern bulbs could deprive people from sleep and campaigners have expressed concerns about the dangerous chemicals they contain .
Both CFls and LEDs require conversion from AC current to DC to operate. In CFLs, the direct current to drives a high-frequency AC source which powers the lamp. Dimming by decreasing the voltage or power supplied to the lamp is not possible. In the LED, the direct current drives a controller which regulates the power supplied to the LED. Dimming by decreasing the voltage or power is not possible. Dimmings of LEDs is accomplished in the controller, via an external control source.
CFLs and LEDs also suffer the following disadvantages:
Incandescent lamp basics
Incandescent lights work by heating a thin tungsten wire to temperatures of around 2700°C. The 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 colour.
The advantage of the incandescent lamp is that it can be powered directly from the supply without the need for converters and controls. The basic design has remained the same over 100 years – a resistive filament enclosed in an evacuated bulb. The light is powered directly form the supply, and current flowing through the filament causes it to heat up to an incandescent state. The spectrum of the lamp is shown in Fig. 1.The main disadvantage of mass-produced incandescents is the low efficiency of conversion of electrical energy to light. In mass-produced lamps, more than 95% of the input energy is converted to heat rather than to light, meaning that incandescents have efficiencies of the order of 3 – 6%.
Whereas the luminous efficiency of conventional incandescent lamps is between 2 and 3%, that of fluorescents (including CFLs) is between 7 and 15%, and that of most compact LEDs between 5 and 15% (see Table 1). With an energy efficiency of <5%, the incandescent is at the bottom of the scale. It is interesting that even the most efficient technology, the LED, has an efficiency of only 15%, which means that 85% of the energy is wasted as heat. One could say that, even in the most efficient artificial lighting system, >80% of the energy input is turned to heat.
The new two-stage incandescents could reach efficiencies as high as 40%, according to researchers.
|Light source||Overall luminous efficiency (%)|
|Incandescent||2 – 3,5|
|Compact fluorescent||7 – 15|
|LED||5 – 15|
The key is to create a two-stage process, the researchers report. The first stage involves a conventional heated metal filament, with all its attendant losses. But, instead of allowing the waste heat to dissipate in the form of infrared radiation, secondary structures surrounding the filament capture this radiation and reflect it back to the filament to be re-absorbed and re-emitted as visible light, as illustrated in Fig. 2.
These structures, a form of photonic crystal or band gap material, are made of abundant elements and can produced using conventional material-deposition technology . In this system, the desired visible wavelengths pass through the material and out of the lamp, but the infrared wavelengths are reflected as if from a mirror. They then travel back to the filament, adding more heat that then gets converted to more light. Since only the visible ever gets out, the heat just keeps bouncing back in toward the filament until it finally ends up as visible light. 
Photonic crystals or photonic band gap (PBG) material
Photonic crystals were initially used in quality fibre optic applications such as filters and other devices, but increasing use in end-user applications has made possible the manufacture of cheap, one-dimensional PBG layers. Photonic crystal structures are used widely as anti-reflecting coatings which dramatically decrease the reflectance from the surface and are used to improve the quality of the lenses, prisms and other optic components.
Photonic crystal materials
Photonic band gap (PBG) material has a perfect crystal lattice structure that blocks the propagation of light of certain wavelengths. Materials used include silicon, germanium, gallium arsenide and indium phosphide, all of which are already in use in the semiconductor industry. Nanotechnology makes the manufacture of crystal structures of the desired parameters an easy process.
State of development
The technology is reported as being at proof-of-concept stage , with several laboratory demonstration models tested successfully. The models show efficiencies two to three times as high as the standard incandescent lamp and, in some cases, higher than mass-produced CFLs. Further development is taking place and, as with most products, efficiency is expected to rise and costs are expected to fall as more people become involved in the technology. Researchers expect the fully-developed product to have an efficiency approaching 40%, higher than the best LED technology at the moment.
Sadly, development and production may be hamstrung by legislation, as many countries have placed a blanket ban on the production of all types of incandescent lamp, ignoring the possibility of disruptive changes in the technology itself and favouring CFL and LED development instead. This is an unfortunate feature of regulation, which has the effect of “freezing” technological development.
One can hope that this will develop into a viable product, as the simple plug and play nature of the device has the potential to revolutionise the lighting industry and to remove many of the problems that currently exist with alternative technologies.
 K Kelchner: “Lightbulbs and the lumen”, http://laserboyfriend.blogspot.co.za/2012/09/lightbulbs-and-lumen.html
 S Knapton: “Return of incandescent light bulbs as MIT makes them more efficient than LEDs”, http://www.telegraph.co.uk/science/2016/03/12/return-of-incandescent-light-bulbs-as-mit-makes-them-more-effici/
 D Chandler: “A nanophotonic comeback for incandescent bulbs?” MIT News,
11 January 2016.
Send your comments to firstname.lastname@example.org