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Light-emitting diodes were invented in the 1920s. Today, LEDs come in various colours, brightness and wavelength—visible, ultraviolet and infrared. LEDs have a lot of advantages over traditional lighting including low energy consumption, long lifetime, small size and robustness. Everyone is looking at the next wave of lighting luminaires that will produce smart lighting with LED and organic light emitting diode (OLED) systems.

LEDs are more rugged, resembling something closer to hard plastic, than thin glass. While fluorescent lights have been justly praised for offering greater efficiency than incandescent bulbs, LEDs are more effiient and last longer than any other lighting source in the market, making them the next logical step. They are also environmentally sound, since their manufacturing does not require toxic substances such as mercury.

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Consumers are already getting their first taste of LED technology wit indoor/outdoor festival lights. Experts expect that a new wave of lighting devices based on LEDs and solid-state lighting will supplant the common light bulb in coming years, leading to vast environmental, energy and cost benefits, as well as innovations in healthcare, transport systems, digital displays and computer networking.

A new report fins that the market for LEDs is set to explode in the next ten years, surpassing even compact fluorescent light bulbs as the ultimate energy-efficient lighting option. According to a study, by 2020, LEDs will cover 46 per cent of the $4.4 billion US market for lamps in the commercial, industrial and outdoor stationary sectors, driven by the overall push toward energy efficiency. That’s a big jump, considering that LEDs now capture only two per cent of the lighting market, according to estimates.

Advantages
LED bulbs typically last 50,000 hours—twice as long as fluorescent—and are up to twice as efficient as fluorescent which are again four to six times more efficient than incandescent. Further, unlike fluorescent or incandescent bulbs, LED tubes do not get very hot. According to a report, incandescent bulbs only convert about four to six per cent of the energy they receive into light; the rest is wasted as heat. While fluorescent bulbs can raise the temperature in a room by up to two degrees resulting in increased cooling load for buildings, LEDs don’t raise the temperature at all.

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However, smart LEDs should not be seen as just a replacement technology for compact fluorescent lamps (CFLs) and incandescent lamps, but as a serious disruptive technology. Regular bulbs can only be turned on or off, whereas LEDs can be tuned like a radio.

LEDs have novel capabilities that make them extremely useful when going beyond the replacement paradigm. As an alternative to the traditional incandescent light bulb, LED lights provide significant energy-savings. They can be 2000 per cent more effcient than conventional light bulbs and 500 per cent more efficient than compact fluorescent bulbs.

Engineers and scientists predict that widespread use of LEDs over the course of ten years would save more than $1000 billion in energy costs, eliminate the need for nearly a billion barrels of oil over ten years, and lead to a substantial reduction in emissions of carbon dioxide—the most common greenhouse gas. If the entire world was to switch over to LEDs, there would be tremendous savings in energy costs and an increase in energy security. In addition to their high efficiency and long lifespan, LEDs do not require ballast and do not contain toxic mercury, which means disposing them of poses fewer health and environmental hazards.

Growing applications
In contrast to conventional light sources, a number of new dimensions have opened due to the unique controllability of LEDs. These include control over the emission spectrum, colour temperature, polarisation, temporal modulation, hue and spatial emission pattern. These controllable next-generation LED sources, called smart lightings, will result in tremendous benefits to the society and humankind. In general, applications of LEDs in different walks of life include:

Biology and imaging. Leapfrog advances in quantitative biology, particularly the rapid identification and counting of biological cells through adaptive and fully-tunable reflectance and fluorescence imaging.

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Display systems. Liquid-crystal-displays and projectors with unprecedented efficiency and brilliancy (hug colour gamut) through polarisation-controlled lighting sources.

Transportation. Enhanced visibility (less glare) and safety through polarisation-controlled headlights, temporal-controlled communicating headlights/brake lights/trafficlights, and interactive roadways.

Communications. Fundamentally new modes of broadcasting, communications and sensing through temporal control of solid-state light sources.

Human factors. Reduced dependency on sleep-inducing pharmaceuticals, prevention of certain cancers and higher quality of life.

Agriculture. Efficient plant growth in non-native regions (including space), non-native seasons and revolutionised indoor agriculture and urban indoor vertical farming or sky farming.

Limitations
So far, despite the positive forecast, there remain short-term financial and technological obstacles to the market success of LEDs, with the biggest problem being price. LED tubes cost anywhere between $50 and $100, compared to $2-$10 for fluorescent.

The other roadblock frequently cited by electrical engineers and facilities managers is brightness; they are concerned that occupants will complain that the lights are not bright enough. Both problems are being addressed by LED manufacturers, who are researching ways to increase the luminance of LEDs and cut costs.

Recent developments
Researchers have developed and demonstrated a new type of LED with significantly improved lighting performance and energy efficiency The new polarisation-matched LED exhibits an 18 per cent increase in light output and a 22 per cent increase in wall-plug efficiency,which essentially measures the amount of electricity that the LED converts into light. The new device achieves a notable reduction in ‘efficiency-droop’—a phenomenon that provokes LEDs to be most efficient when receiving low-density currents of electricity, but then lose efficiency as higher density currents of electricity are fed into the device. The cause of this droop is not yet fully understood, but studies have shown that electron-leakage is likely a large factor for the problem.

This droop is under the spotlight since today’s high-brightness LEDs are operated at current densities far beyond efficiency-peaks.This challenge has been a stumbling block, because reducing the current densities to values where LEDs are more effiient is unacceptable. However, new LEDs, which have a radically re-designed polarisation-matched active region, tackles this issue and brings LEDs closer to being able to operate efficiently at high current densities.

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Focusing on the active region of LEDs, where the light is generated, researchers discovered that the region contained materials with mismatched polarisation. The polarisation- mismatch possibly causes electron leakage, and therefore a loss in efficiency The researchers discovered that the polarisation-mismatch can be reduced by introducing a new quantum-barrier design. They replaced the conventional gallium indium nitride/gallium nitride (GaInN/GaN) layer of the LED active region with GaInN/GaInN. This substitution allows the layers of the active region to have a better-matched polarisation, resulting in reduced electron-leakage and efficiency-droop.

Although reports suggest that paying more for LEDs would be worth it, as long-term use of LEDs will compensate their operational cost as compared to fluorescent bulbs, still, as with most green products, the long-term cost savings of LEDs won’t necessarily convince users right away. It’s likely to take a while for them to warm up to the idea that they should increase their lighting budget by a few thousand dollars, even if it means reducing their energy bills. Researchers at Purdue University found a way to replace the expensive standard substrate used in LED production—sapphire—with low-cost, metal-coated silicon wafers. The switch would greatly reduce the cost of LED manufacturing, assuming another silicon shortage does not come along.

The way forward
Along with much of the attention being focused on the next-generation energy-efficient lighting—solid-state technologies like LEDs with their vast household as well as industrial applications—companies have also been working on new LED fixture and bulbs that promise to cut overall operational lighting costs by up to 70 per cent. A study predicted that it will take ten years for LEDs to overcome all types of obstacles to their mass adoption.


The author is an associate professor in Department of Physics, S.L.I.E.T., Longowal, District Sangrur, Punjab

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