Shades of grey light

Just when you have flushed out the last incandescent at home, researchers in Japan have modified the blackbody radiation of an incandescent bulb, demonstrating the possibility of 95% electric power to visible-light conversion and paving the way for luminous efficiencies beyond 400 lm/W.

Because visible radiation is typically 10% of the output from an incandescent bulb, with the remaining 90% being infrared (IR) radiation, an emitter should be designed with high visible emissivity and low IR emissivity. Using Kirchhoff's law, modeling shows that a material with high reflectance in the IR wavelength region and low reflectance in the visible region displays a reverse trend in emissivity. By imposing a step-function-like reflectivity onto the surface of the heating material, IR radiation is reduced. The researchers fabricated such a thin-film structure (emitter) by co-sputtering 50 nm thick chromium metal and 50 nm thick chromium oxide onto a copper substrate.

The problem with incandescents was that only 2–5% of total input electrical power is converted to visible light, translating to low luminous efficiencies of 15–20 lm/W. Now that seems like being tackled. So is it worth pursuing this line? Why?

Unlike LEDs, incandescent lamps require no external regulating equipment, are inexpensive to produce, and work on either alternating or direct current over a wide range of applied voltage values. So perhaps we must take another look.

Almost 200 years have passed since the creation of the first incandescent light; however, there is ample scope for new discoveries and new applications in incandescence. Comes down again to, no black and whites only greys in life!