What is the most energy-efficient way to use a light bulb? In other words, if you use a certain bulb every twenty minutes or so, is it best to leave it on all the time?
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Aristocles
ANSWERS: 3
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For an incandescent light bulb, there is no difference in energy consumption between when you turn it on and when it's been running, so you shouldn't leave it on unnecessarily. If the bulb is a fluorescent or halogen type, you might want to leave it on.
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For energy efficiency, the solution is undoubtedly to turn it off whenever you don't need it. The slight surge of current when you turn it back on again represents only a second or so of usage. The reason for leaving an incandescent light bulb on is financial, not energy, efficiency. When it is turned on, a surge current larger than the normal operating flows and the filament is heated from room temperature to over 2000C in a fraction of a second. This shock shortens the bulb's life by the equivalent of a large number of minutes of usage - not sure how many. You may notice that bulbs nearly always blow as they are turned on because of this shock effect. If you turn the light on and off, you will therefore save energy, but the bulb will blow sooner, and the cost in extra bulbs may be more than the electricity saved.
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Every light bulb has a "break even" time. that is the time at wich if you're leaving for shorter than that amount of time, it's more efficient to leave the bulb on. for most bulbs the break even time is about a third of a second, for the straight floruecent bulbs it's just under 30 seconds.
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