Turning off lights to save money, energy and even the planet, has become an accepted piece of folk wisdom the world over. According to the U.S. Department of Energy, electric lighting in the U.S. accounts for 20 percent of the country’s energy consumption. But other versions of popular wisdom challenge this cost saving. The contrarians note that all forms of electric lighting deteriorate as they are switched on and off. The shortened operating life and subsequent replacement cost of any item of lighting may be greater than the cost of electricity saved. According to experts at the Palo Alto-based Electric Power Research Institute, if you want to save money, switch off the lights.
Light amounts to just 10 percent of the energy produced by an incandescent bulb. The remainder is heat. Heat production consumes more electricity than light production so you can save money by switching off these bulbs when they are not in use. Saved electricity costs will be greater than the bulb’s replacement cost. The traditional incandescent bulb consists of a tungsten filament that is eroded slowly by the heat. When the filament breaks the bulb is burned out.
Halogen incandescent bulbs have become a popular replacement for the traditional bulb. They work on the same principle of producing light from a heated tungsten filament. But in this case, halogen gas inside the bulb keeps the filament solid as it heats. The bulb is smaller than the traditional variety, produces a brighter light and does not burn out so quickly. It is also cost-effective for the user to switch off the halogen light when it is not in use.
After they are switched on, fluorescent lights require a small amount of electrical ballast to start up. The start-up electrical current is slightly greater than the current used by the light to operate. The U.S.Department of Energy advises that it is cost effective to leave a fluorescent light on when leaving a room for less than 15 minutes. At times of peak electricity demand, this period can fall to five minutes. Other sources also suggest the five minute rule, writes John Matson, in "Scientific American." But the California Energy Commission disagrees with this thinking, calling it an urban myth. The power surge lasts only a couple of seconds after switching on the light. Switching fluorescent lights on and off may affect the length of their operating life, the commission notes, but the energy saving is greater than their replacement cost.
The lifetime of light emitting diode lights is not affected by the electricity supply switching off and on. LED lights are composed of crystals of semiconductor compounds such as gallium arsenide. They fit into an electrical circuit like filament bulbs and fluorescent lights. But the semiconductor produces mostly light and little heat, making it a cost-effective light to operate. LED lights are bright almost instantaneously after being switched on and do not deteriorate when switched on and off. In common with bulbs and fluorescent lights, it is cheaper to switch LED lights off when they are not in use.
- U.S. Department of Energy: Energy Savers; When to Turn off Your Lights
- California Electric Commission: Urban Myth – Leaving a Fluorescent Light Turned on is Cheaper than Turning it Off and On
- European Council for an Energy Efficient Economy: Lighting Energy Consumption Trends and Conservation Opportunities in U.S. Buildings
- Scientific American: Does Turning Fluorescent Lights Off Use More Energy Than Leaving Them On?
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