For all those that are interested in light, and regret the prohibition of the incandescent lamp, 2016 may have started promising. A publication in the scientific journal „Nature Nanotechnology“ led to headlines as enthusiastic as „The resurrection of the incandescent lamp“. Scientists at the Massachusetts Institue of Technology (MIT) have managed to drastically increase the luminous efficiency of an incandescent lamp.
The idea behind it sounds simple and elegant: The tungsten filament is replaced through a tungsten sheet as a thermal emitter. This is „sandwiched“ by a material which, as a result of multiple layers of coating with nanotechnology, only lets the visible part of the light through and can reflect the infrared heat radiation back to the incandescent material, thus heating it up more and increasing the luminous output.
The luminous efficiency of 40% which is often quoted, and would surpass current flourescent and LED lamps by far, hasn´t been reached in this experiment, it has only been calculated as a maximum efficiency for an optimized stack. However, the experimental prototype was able to reach an efficiency that came close to energy saving lamps and LED lights.
So, can we expect to soon have a good and healthy light, with the potential to save vast amounts of energy? As much as we would like this to be the case, some questions remain unresolved, and should not be overlooked:
The goal of the scientists is to tailor the spectral emission of the lamp to the sensitivity of the human eye, reflecting all the invisible parts of the light spectrum. This would eliminate the complete infrared radiation, which, while not being needed for vision itself, plays an important role in the regeneration of the eye tissue. Should this optimized construction prove possible, we would get a light source that, not unlike LED or CFL (compact fluorescent lamps), only provides a part of the natural light spectrum, even though it is probably that this part will show a more natural and healthyer distribution of wavelengths than the alternatives. The color rendering index (CRI) of the experimental lamp was better than that of CFL and of most LED lights, but with a CRI of 95, still fails to hit the gold standard: natural daylight with a CRI of 100 or halogen lamps with a CRI of 99.
The published essay is an experimental proof-of-concept and shows that the spectrum of luminous output can be tailored to specific needs (besides lighting, this would be interesting for the opimizing of photovoltaic systems). Lifespan and thermal stability of the materials used in the experiments are far from being ready for the market.
The scientists claim that the materials needed are both common and cheap, as well as ameanable to large scale production. However, nanotechnology is not without controversy. Nanoparticles can pass the blood-brain barrier and have the potential of being far more toxic than larger parts of the same chemicals. Even with the billions spent every year to investigate the properties of nanoparticles, research usually focsses on the potential economic profit. More than a decade after the first warnings about adverse effects have been published, there still seems to be insufficient data to determine the safety for people working in the production of nanoparticles, how to safely dispose of nanowaste, and how to avoid the accumulation of nanoparticles in nature.
On the bright side, it is reassuring that headlines like „resurrection of the incandescent“ seem to catch people´s interest; a sign that more and more people are aware that the lights we are almost forced to buy these days are neither good for health nor for well-being. But it would be sad if we got the incandescent lamp back with an incomplete spectrum combined with an incalculable risk for both producers and environment.
We will continue to watch the developement, and in the meantime continue to use the halogen lamps that are still available. As for lowering energy consumption? We simply switch off the lights when leaving the room…