Green Promise Seen in Switch to LED LightingBy Elisabeth Rosenthal and Felicity BarringerTo change the bulbs in the 60-foot-high ceiling lights of Buckingham Palaces grand stairwell, workers had to erect scaffolding and cover precious portraits of royal forebears.So when a lighting designer two years ago proposed installing light emitting diodes or LEDs, an emerging lighting technology, the royal family readily assented. The new lights, the designer said, would last more than 22 years and enormously reduce energy consumption and carbon dioxide emissions a big plus for Prince Charles, an ardent environmentalist. Since then, the palace has installed the lighting in chandeliers and on the exterior, where illuminating the entire facade uses less electricity than running an electric teakettle.In shifting to LED lighting, the palace is part of a small but fast-growing trend that is redefining the century-old conception of lighting, replacing energy-wasting disposable bulbs with efficient fixtures that are often semi-permanent, like those used in plumbing.Studies suggest that a complete conversion to the lights could decrease carbon dioxide emissions from electric power use for lighting by up to 50 percent in just over 20 years; in the United States, lighting accounts for about 6 percent of all energy use. A recent report by McKinsey & Company cited conversion to LED lighting as potentially the most cost effective of a number of simple approaches to tackling global warming using existing technology.LED lighting was once relegated to basketball scoreboards, cellphone consoles, traffic lights and colored Christmas lights. But as a result of rapid developments in the technology, it is now poised to become common on streets and in buildings, as well as in homes and offices. Some American cities, including Ann Arbor, Mich., and Raleigh, N.C., are using the lights to illuminate streets and parking garages, and dozens more are exploring the technology. And the lighting now adorns the conference rooms and bars of some Renaissance hotels, a corridor in the Pentagon and a new green building at Stanford.LEDs are more than twice as efficient as compact fluorescent bulbs, currently the standard for greener lighting. Unlike compact fluorescents, LEDs turn on quickly and are compatible with dimmer switches. And while fluorescent bulbs contain mercury, which requires special disposal, LED bulbs contain no toxic elements, and last so long that disposal is not much of an issue.It is fit-and-forget-lighting that is essentially there for as long as you live, said Colin Humphreys, a researcher at Cambridge University who works on gallium nitride LED lights, which now adorn structures in Britain.The switch to LEDs is proceeding far more rapidly than experts had predicted just two years ago. President Obamas stimulus package, which offers money for green infrastructure investment, will accelerate that pace, experts say. San Jose, Calif., plans to use $2 million in energy-efficiency grants to install 1,500 LED streetlights.Thanks in part to the injection of federal cash, sales of the lights in new solid state fixtures a $297 million industry in 2007 are likely to become a near-billion-dollar industry by 2013, said Stephen Montgomery, director of LED research projects at Electronicast, a California consultancy. And