Wednesday, April 27, 2011

Green UV Sterilization: Switching on LEDs to Save Energy and the Environment

ScienceDaily (Apr. 27, 2011) — Ultraviolet light can safely sterilize food, water and medical equipment by disrupting the DNA and other reproductive molecules in harmful bacteria. Traditionally, mercury lamps have supplied this UV light, however mercury release from power generation and lamp disposal have generated discussion of harmful environmental impact. A potentially energy efficient and non-toxic alternative is the light-emitting diode, or LED, which can be made to emit at almost any desired wavelength. LEDs are also more rugged and operate at lower voltages than glass containing mercury bulbs.

Thus, LEDs are more compatible with portable water disinfection units, which could also be solar-powered and used in situations where centralized facilities are not available, such as disaster relief. LEDs currently require a lot of electricity to produce UV light, but researchers from around the world are focused on improving this efficiency.

LEDs are semiconductor devices that operate in much the same way as the tiny elements on a computer chip. The difference is that some of the electrons flowing into an LED are captured and release their energy as light. Because these are solid materials rather than gas-filled bulbs, LEDs are more compact and durable than alternative light sources. The first commercial LEDs were small red indicator lights, but engineers have developed new materials that emit in a rainbow of colors. Nitride-based LEDs are the most promising for pushing beyond the visible into the ultraviolet. Some of these UV LEDs are already being used in the curing of ink and the testing for counterfeit money, but for sterilization, shorter wavelength light is required. These short wavelength, or "Deep UV" LEDs, present a number of technical challenges and are predominantly implemented in highly-specialized disinfection systems in industrial and medical applications, as well as other non-disinfection markets.

The Joint Symposium on Semiconductor Ultraviolet LEDs and Lasers at CLEO: 2011 will feature several talks addressing these challenges, while highlighting current efforts to improve the efficiency of nitride-based LEDs. Max Shatalov of Sensor Electronic Technology in Columbia, S.C., will report an improved design for making high-power UV LEDs that would be especially good for knocking out bacteria. From the birthplace of nitride (blue and white) LEDs, Motoaki Iwaya from Meijo University in Japan will describe a joint effort with Nagoya University to extend the range and improve the efficiency of UV LEDs.

The application of these UV LEDs is also being pursued in a related CLEO: 2011 session. Gordon Knight from Trojan Technologies in Canada will review advances in production of novel UV light sources, along with necessary validation procedures for verifying the operation of water disinfection systems in a one-hour tutorial.

This research will be presented at the Conference on Lasers and Electro-Optics (CLEO: 2011), May 1 -- 6 at the Baltimore Convention Center.


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