Switch to New Luminescence

It’s time to bid farewell to the good old light bulb; environment-friendly LEDs promise to become cheaper.

The incandescent bulb is one of humanity’s most useful inventions, but this ubiquitous product is now nearing the end of its life. It may soon be replaced by a product that is yet to be used widely for lighting, but otherwise has many applications. It is called the Light Emitting Diode, or LED for short. LED lamps are not used in large numbers because they are inefficient and expensive. But scientists are now making the vital breakthroughs that would make them cheap and efficient enough to be used in mass scale within two or three years.

LEDs are now so expensive that they can be used only for special applications. In the US, for example, an LED bulb costs $100. This makes it beyond the reach of even the rich. There are several reasons for LEDs being so expensive, one of the most important being the complicated manufacturing process. But scientists at Purdue University have now developed a simplified process that can greatly reduce the price. Purdue’s efforts are among the latest and most interesting, but engineering teams from other labs are also consistently reporting breakthroughs.

In the lab of Shuji Nakamura — the world’s leading expert on LEDs — at the University of California in Santa Barbara, engineers are developing LEDs with efficiencies several times that of the incandescent bulb, and even beyond the widely-used Compact Fluorescent Lamp (CFL). At the Rensselaer Polytechnic Institute in New York, engineers have created green LEDs — a problem area so far in making efficient white LED bulbs — that are far more efficient. At Boston University, engineers are developing another revolutionary method of creating LEDs that will lead to further efficiencies. Says Timothy Sands, director of the Birck Nanotechnology Centre in Purdue University: “We could in the near future make LEDs that cost only $5 per bulb.”

In spite of our technological advances, human beings have not yet developed a light source that is efficient, cheap and environment friendly. The incandescent bulb, despite having served a century of distinguished service, is a lousy product in terms of efficiency. From a physical point of view, it is more a heating device than a light source. About 90 per cent of the electrical energy input to the incandescent bulb is converted to heat that goes as waste. The impact of this problem on our energy bill is enormous, if we consider that 20 per cent of the world energy production goes towards lighting, the single most important consumer of electricity.

Engineers in recent times have come up with two kinds of bulbs: the fluorescent lamp and the CFL. Both are very energy-efficient — the CFL the more so — but not very environment friendly. CFLs contain mercury and are already banned for landfills in developed countries. Both can at best be temporary solutions while we develop other more efficient and benign products. And nothing seems more promising than the LED.

Everybody who owns a television set would have seen an LED. It is the small red dot that glows to indicate that the television set is on. While it is fine for this application, it has had some serious technical issues to overcome when used for lighting up buildings. One problem is the manufacturing. Currently, LEDs are manufactured using an expensive material called sapphire as a substrate for gallium nitride, the light emitting substance. This substrate is then removed after manufacture. This is where the Purdue team has made the breakthrough by substituting sapphire with silicon, the material of the electronic age.

The use of silicon immediately creates possibilities of mass manufacture, and the technique is not very far away from commercialisation. Says Sands: “There are some problems to be solved before commercialisation but they are not killer problems.” This technique is expected to reduce the price considerably, but the high cost of manufacturing is only one of the issues dogging LEDs. Another critical problem is the so-called “green gap”, where the efficiencies of the bulb drop in the green part of the spectrum. This problem lies in the way of efficient and powerful white LEDs, because white light is made by combining green, blue and red LEDs.

The green gap problem is not yet completely solved, but researchers at the Rensselaer Polytechnic and UC Santa Barbara are now closer to solving it. “There is nothing in theory that would prevent us from producing an LED bulb that is almost 100 per cent efficient,” Nakamura had told The Telegraph some time ago.

Leading labs have now reached around 60 per cent efficiencies, and less for high-power LEDs. The goal of the US government is to reach efficiencies of 50 per cent.

With the US and some European countries formulating deadlines to phase it out, perhaps it’s time to bid the bulb goodbye.

Sources: The Telegraph (Kolkata, India)

This entry was posted on Tuesday, July 29th, 2008 at 10:20 pm and is filed under Featured. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

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