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Independent Professional: Experienced educator and management consultant for engineering educational institutions, researcher, trainer, technical consultant on sustainable technologies, related to cement manufacturing and characterisation, using industrial and agricultural wastes in cement and concrete, durability of concrete and fuel cell power.

Thursday, February 19, 2009

Low-cost LED:

Dr J D Bapat

We are very close to achieving highly efficient, low cost white LEDs that can take the place of both traditional and currently available low energy light bulbs. That won’t just be good news for the environment. It will also benefit consumers by cutting their electricity bills. In addition to the environmental and cost benefits of LEDs, the technology is expected to enable a wide range of advances in areas as diverse as healthcare, transportation systems, digital displays and computer networking.

A light-emitting diode (LED) is a semiconductor diode that emits light when charged with electricity. The LEDs are used for display and lighting in a whole range of electrical and electronic products.

A new way of making LEDs could see household lighting bills reduced by up to 75% within five years. Gallium Nitride (GaN), a man-made semiconductor used to make LEDs (light emitting diodes), emits brilliant light but uses very little electricity. Although GaN was first produced over 30 years ago, it is only in the last ten years that GaN lighting has started to enter real-world applications. Currently, the brilliant light produced by GaN LEDs is blue or green in colour. A phosphor coating is applied to the LED to transform this into a more practical white light. Until now high production costs have made GaN lighting too expensive for wide spread use in homes and offices.

With funding from the Engineering and Physical Sciences Research Council (EPSRC), the Cambridge University based Centre for Gallium Nitride has developed a new way of making GaN which could produce LEDs for a tenth of current prices.
The Cambridge Centre for Gallium Nitride was established in 2000.


The Engineering and Physical Sciences Research Council (EPSRC) is the UK’s main agency for funding research in engineering and the physical sciences. The EPSRC invests around £740 million a year in research and postgraduate training, to help the nation handle the next generation of technological change. The areas covered range from information technology to structural engineering, and mathematics to materials science. This research forms the basis for future economic development in the UK and improvements for everyone’s health, lifestyle and culture. EPSRC also actively promotes public awareness of science and engineering. EPSRC works alongside other Research Councils with responsibility for other areas of research. The Research Councils work collectively on issues of common concern via Research Councils UK.

GaN LEDs are currently grown on 2-inch sapphire. In comparison to that, it is possible to produce 10 times as many LEDs on a 6-inch silicon wafer. The processing costs remain essentially the same. The 6-inch silicon wafer is much cheaper to produce than a 2-inch sapphire wafer. Together these factors result in a cost reduction of about a factor of 10. This lower cost method could mean cheap mass produced LEDs become widely available for lighting homes and offices in the next five years.

Low-cost LED save huge energy:

Dr J D Bapat

Based on current results, GaN LED lights in every home and office could cut the proportion of electricity used for lights from 20% to 5%. That means we could close or not need to replace many power stations.

A GaN LED can burn for 100,000 hours. Thus, on average, it needs replacement only after 60 years. Unlike currently available energy-saving bulbs, GaN LED does not contain mercury so disposal is less damaging to the environment. GaN LEDs also have the advantage of turning on instantly and being dimmable.

GaN LEDs, used to illuminate landmarks like Buckingham Palace and the Severn Bridge, are also appearing in camera flashes, mobile phones, torches, bicycle lights and interior bus, train and plane lighting.

If all of the world's light bulbs were replaced with LEDs for a period of 10 years, the following benefits would be realized:

  • Energy savings of 1.9 × 1020 joules
  • Electrical energy consumption would be reduced by terawatt hours
  • Financial savings of $1.83 trillion
  • Carbon dioxide emissions would be reduced by 10.68 gigatons
  • Crude oil consumption would be reduced by 962 million barrels
  • The number of required global power plants would be reduced by 280


Low-cost LED Long term applications:

Dr J D Bapat

Parallel research is also being carried out into how GaN lights could mimic sunlight to help 3million people in the UK with Seasonal Affective Disorder (SAD). Ultraviolet rays made from GaN lighting could also aid water purification and disease control in developing countries, identify the spread of cancer tumours and help fight hospital ‘super bugs’.

• Cancer surgery: Currently, it is very difficult to detect exactly where a tumour ends. As a result, patients undergoing cancer surgery have to be kept under anaesthetic while cells are taken away for laboratory tests to see whether or not they are healthy. This may need to happen several times during an operation, prolonging the procedure extensively. But in the future, patients could be given harmless drugs that attach to cancer cells, which can be distinguished when a blue GaN LED is shone on them. The tumour’s edge will be revealed, quickly and unmistakably, to the surgeon.

• Water purification: GaN may revolutionise drinking water purification in developing countries. If aluminium is added to GaN then deep ultra-violet light can be produced and this kills all viruses and bacteria, so fitting such a GaN LED to the inside of a water pipe will instantly eradicate diseases, as well as killing mosquito larvae and other harmful organisms.

• Hospital-acquired infections: Shining a ultra-violet GaN torch beam could kill viruses and bacteria, boosting the fight against MRSA and C Difficile. Simply shining a GaN torch at a hospital wall or trolley, for example, could kill any ‘superbugs’ lurking there.

Deployed on a large scale, LEDs have the potential to tremendously reduce pollution, save energy, save financial resources and add new and unprecedented functionalities to photonic devices. These factors make photonics what could be termed a benevolent tsunami, an irresistible wave, a solution to many global challenges currently faced by humanity and will be facing even more in the years to come. It will open up a new chapter in photonics: Smart lighting sources that are controllable, tunable, intelligent, and communicative.

References
:

(1) Schubert E. F. and Kim J. K. "Transcending the Replacement Paradigm of Solid-State Lighting", Optics Express, Vol. 16, Issue 6, December 22, 2008

(2)
Engineering and Physical Sciences Research Concil (EPSRC), UK, press release 29 Jan 2009

(3) Science Daily, December 20, 2008