http://www.economist.com/node/16886228
Energy conservation Not such a bright idea Making lighting more efficient could increase energy use, not decrease it Aug 26th 2010 SOLID-STATE lighting, the latest idea to brighten up the world while saving the planet, promises illumination for a fraction of the energy used by incandescent or fluorescent bulbs. A win all round, then: lower electricity bills and (since lighting consumes 6.5% of the world’s energy supply) less climate-changing carbon dioxide belching from power stations. Well, no. Not if history is any guide. Solid-state lamps, which use souped-up versions of the light-emitting diodes that shine from the faces of digital clocks and flash irritatingly on the front panels of audio and video equipment, will indeed make lighting better. But precedent suggests that this will serve merely to increase the demand for light. The consequence may not be just more light for the same amount of energy, but an actual increase in energy consumption, rather than the decrease hoped for by those promoting new forms of lighting. The light perceived by the human eye is measured in units called lumen-hours. This is about the amount produced by burning a candle for an hour. In 1700 a typical Briton consumed 580 lumen-hours in the course of a year, from candles, wood and oil. Today, burning electric lights, he uses about 46 megalumen-hours—almost 100,000 times as much. Better technology has stimulated demand, resulting in more energy being purchased for conversion into light. That, at least, is the conclusion of a study published in the Journal of Physics D: Applied Physics by Jeff Tsao of Sandia National Laboratories in New Mexico and his colleagues. They predict that the introduction of solid-state lighting could increase the consumption of light by a factor of ten within two decades. To work out what solid-state lighting would do to the use of light by 2030, Dr Tsao and his colleagues made some assumptions about global economic output, the price of energy, the efficiency of the new technology and its cost. Assuming that, by 2030, solid-state lights will be about three times more efficient than fluorescent ones and that the price of electricity stays the same in real terms, the number of megalumen-hours consumed by the average person will, according to their model, rise tenfold, from 20 to 202. The amount of electricity needed to generate that light would more than double. Only if the price of electricity were to triple would the amount of electricity used to generate light start to fall by 2030. Dr Tsao and his colleagues see no immediate end to this process by which improvements in the supply of light stimulate the desire for more—rather as the construction of that other environmental bête noire, roads, stimulates the growth of traffic. Even now, the interiors of homes and workplaces are typically lit at only a tenth of the brightness of the outdoors on an overcast day, so there is plenty of room for improvement. And many outdoor areas that people would prefer to be bright at night remain dark because of the expense. If money were no object, some parts of the outdoors might be illuminated at night to be as bright as day. It is worth remembering that when gas lights replaced candles and oil lamps in the 19th century, some newspapers reported that they were “glaring” and “dazzling white”. In fact, a gas jet of the time gave off about as much light as a 25 watt incandescent bulb does today. To modern eyes, that is well on the dim side. So, for those who truly wish to reduce the amount of energy expended on lighting the answer may not be to ban old-fashioned incandescent bulbs, as is the current trend, but to make them compulsory.
