Avnet’s Eskow sheds light on UV LEDs

In a keynote address titled “Beyond the Rainbow’s Edge,” Carey Eskow, director of LightSpeed, the solid-state lighting and LED business unit of Avnet Electronics Marketing, treated attendees at EDN’s September 29 “Designing with LEDs” workshop to a history of ultraviolet, bringing us from 1800 up to today’s emergence of UV LEDs.

Eskow credited Herschel Wilhelm, a composer, philosopher, physicist, and astronomer, as the first to look beyond the rainbow’s edge. Wilhelm in 1800, in an attempt to determine the density of a filter, used thermometers to examine the temperatures of the various colors of the spectrum. He noted that temperature increased from blue to red and that, in fact, the highest temperatures occurred beyond visible red light. Wilhelm had discovered “heat rays”—or infrared. This discovery led Johann Wilhelm Ritter, who expected to see polarity in nature, to investigate what might lie beyond the blue edge of the rainbow. In 1801, using silver chloride in place of thermometers, he discovered “chemical rays”—or ultraviolet.

Eskow said that today, most practical applications for UVB (315 to 280 nm) and UVC (280 to 100 nm) rays are generated by mercury-discharge UV lights. Such lights, he said, are broad-spectrum emitters, with 60% of their power emitted as heat. The excess heat can cause damage to films and paint being cured through UV exposure when mercury-discharge lamps are employed. In addition, such lamps offer limited lifetimes, cannot be switched on or off easily, and average only about 5% wall-plug efficiency.

The emergence of UV LEDs is solving the problems of mercury-discharge lamps, Eskow said, adding that available UV LED products offer a characteristically narrow, well-defined output, have a near instantaneous pulse response, emit no IR, come in small form factors, and offer lifetimes 8x to 10x those of mercury-discharge lamps.

Applications for UV LEDs, Eskow said, include non-line-of-site communications (a modulated skyward-pointing cone of UV light is jam proof), biohazard detection (disease agents such as anthrax have specific UV fingerprints), precision curing and printing (UV LEDs can be mounted on a print head), and medical diagnosis (UV-sensitive dyes can be used to distinguish between apoptosis, or natural cell death, and necrosis, cell death caused by disease or trauma).

A partial list of companies making high-power UV LEDs includes Luminus Devices Inc., Nichia, LedEngin, Enfis, and Sensor Electronic Technology Inc., Eskow said.

For more on LEDs, see Test & Measurement World’s September issue.

Update: Margery Conner adds some specifics about UV LED manufacturers’ offerings.

Update (10/4/2010): The original post misstated the date of the event. The date has been corrected. In addition, the post has been edited to reflect the full title of Mr. Eskow.