Is it more energy-efficient to let a light bulb burn for a short period of time, or to turn it off and then on again? I read once that the surge in power when a bulb is turned on is equal to letting the bulb burn for a while?
A: It is more energy efficient to turn the light off than to leave it on. Energy is measured with respect to time. The unit used to measure electrical energy is the kilowatt-hour or thousand-watt-hour, the amount of power or watts that you use in one hour. The momentary or millisecond or less surge of electricity required to start your light bulb will not impact your energy cost, but leaving it on all the time will. With the rising cost of energy, it’s probably a good idea to turn the lights out when you are not using it. (Not to mention the pollution impact, less energy use, less emissions from power plants.) Turning the lights on and off a lot will impact your lamp life, however. If you compare the number of bulb(s) you need to buy versus the cost to let the light burn all the time, it will still probably be cheaper to turn the lights off. (http://www.plant.bf.umich.edu/utilities/energy_management/energy-tips/)