Does it use more electricity to turn lights on and off or to leave them on if it is only for a short period of time?

Answer 1

This used to be a valid question with older fluorescent fixtures, but not anymore. A light that is off doesn't use power and it doesn't use extra power when turning on, so turn it off to save power. It depends what you want to consider. If you throw bulb life into the mix (most bulbs fail due to thermal cycle fatigue) then you might be better off leaving the light on. Incandescent lamps have substantially higher inrush current before the filament heats up. This probably does not amount to enough to significantly increase the operating cost, however it reduces the life of the bulb. Incandescent light failure is almost always when cycling the lamp on.

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It's always best to turn the lamp off when it isn't needed. The extra power from the inrush occurs over an extremely short time and the energy used is minimal.

On 240 volts suppose the inrush is 10 amps for 1/20 second (it is probably much less), the energy of the inrush is 2400/20 watt-seconds, 120 watt-seconds, which is the same as leaving it switched on for 1.2 seconds.

On that basis you should turn it off if you plan to be outside that room for 2 seconds or more.

Answer 2

It is better to turn it off, the start up current in a light bulb will never exceed the power consumption over a five minute period. A motor shouldn't even be left on for that same reason. (Yes there is a start up current in a light bulb, it's just extremely small.) Your bulb will last longer if you leave it ON. Its the on/off cycle that kills bulbs. Electricity wise; you may save a few pennies a month by shutting it off. True, bulbs do loose life if constantley turned on and off, but you would have to turn it on and off hundreds of times for this to be an issue. A more serious issue would be where the bulb is located,for example a light bulb next to a door will not last as long as a light bulb in the middle of the room, simply because of the shock from the door closing. It is still best to turn the light off, esspecially if its a long life bulb.

Answer 3

MythBusters (Discovery Channel) actually performed this exercise with various fixtures and bulb types. They found that the initial surge (created when the light is turned on) is the equivalent of that same bulb remaining on for a fraction of a second.

Answer 4

Short answer is no. Old fluorescent fixtures use to have ballasts that required considerable energy to start and warm up, if the light was switched on and off frequently then it would have been better just to leave it on, however this limitation has been solved since the early 1980's.

You are doing yourself no favors by leaving a modern florescent light on

Answer 5

It is never cheaper to leave a light on over turning it off. When ever you use power you pay for it. On some commercial and industrial installations lights are left on. These organizations are on stepped power consumption levels. The more power they use the less they pay for a kilowatt hour. When you pay thousands of dollars a month for power, a few lights do not make much difference to the overall cost.

Answer 6

It uses less energy if it is turned off when not used, and that does not seem to affect the life of the bulb either.

Answer 7

It is better to leave them ON.