Some real-world adventures in LED lighting design
Ron Wilson, EDN’s executive editor, whose regular beat is Practical Chip Design, covered the morning keynote at EDN’s Designing with LEDs Workshop.
Keynoting the EDN Designing with LEDs workshop last week, Cary Eskow, director of Lightspeed-Avnet Electronics Marketing, conducted a quick, edge-of-the-chair tour through the world of LED lighting. Surveying issues and applications, Eskow began in a light socket and ended in a colon.
Eskow started by describing series of interlocking dilemmas. On one hand, he said, US Title 24 regulations require efficient lighting in new structures. And regulations are even stricter in much of the rest of the world—Eskow described the US as almost the last refuge of the incandescent lamp. But while compact florescent lamps (CFLs) have rushed to meet Title 24 requirements, they have run directly into Title 22: a separate regulation that states anything with Mercury content—including CFLs—must be treated as hazardous waste when they are dumped. This Catch-22, Eskow said, opened the door for LED lighting in many applications for which it might otherwise be too expensive.
But then comes another dilemma. Eskow observed that most lighting fixture vendors are basically metal-benders. They are not sophisticated in electronics, and they are used to thinking outside the box in terms of interior design, not electronics design. The speaker worried that these vendors might not see the real opportunities in LED technology, and so would be reduced to differentiating their products on price, not features.
But what features can a light bulb have? On this point Eskow had many ideas. What, for instance, about networked, microcontroller-managed lamps with programmable features, he asked. Dimming is an obvious example of what designers could do with an intelligent lamp controller. A Zigbee-hopping network could detect the presence of people and control lamp intensity to just what is needed in a particular part of a room. But Eskow had more interesting things in mind. He cited, for example, using multi-colored LED clusters with independently-controlled intensity to vary the tint of light.
Then Eskow went into an interesting discussion about color temperature and its influence on human psychology. He pointed out that while light at a color temperature of about 10,000 Kelvin stimulated the hypothalamus and increased productivity in most people, retailers used much warmer light—about 3200 K in the US—to make products attractive, and many people found that 1700 K light promoted sensuality. Eskow suggested as an application example that the Hilton hotel chain, which advertises their dual-use as business hotels in during the week and recreation hotels on the weekend could actually encourage such moods by altering the color-temperature of their lighting—an easy manipulation for a well-designed LED controller. Another example would be a programmable system that would allow retailers to experiment with the impact of color temperature on buying behavior.
Moving on from psychological to more biological applications, Eskow suggested that since it was known that intense light at 472 nm stimulated the opsins in the retina, in turn stimulating the hypothalamus, tuned LED light might act as an artificial version of strong coffee. Perhaps more seriously, he described work in which endoscopists are using narrow-band imaging to examine colon walls for traces of tumors. By varying the wavelength of light, Eskow said, the researchers were able to control the depth below the surface of the colon lining they were examining. So it was possible to develop nearly a 3D image of the interior of the colon wall. Finally, he cited work that suggests that intense blue light can increase blood delivery to a local area, perhaps accelerating healing.
Lest the talk be entirely without warnings, during the Q/A period Eskow warned that in their fascination with the ability of LEDs to produce intense light in very narrow beams, vendors may be moving to very bright light sources too quickly. "Light in the range from UV through blue is known to cause corneal damage," he warned, and intense IR can cause retinal damage. This is not an issue in a proper setting. But the intense narrow-beam LEDs in some devices like flashlights, combined with unsupervised children, could be real trouble."
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