Does it save electricity to keep lights on prier to turning them on and off all the time?

Question

my friend and i keep have an argument about lights she said it's a scientific fact that it saves electricity to keep lights on then turning them on and off when you need them she says that it uses a lot of electricity to turn them on and off but i tried to tell her when you turn a light on it's just another wire touching another wire but she still won't believe me please help me with so prof PLEASE

Answer 1

Your friend is wrong.  That's a myth.

The idea that lights use extra electricity to start up is a myth. You'll save electricity every time you turn the lights off, no matter how short the OFF duration, and whether they're regular lights or fluorescents.

You might have heard that you wear out your lights quicker by cycling them off and on, but that effect is so small it's not worth worrying about, and you can safely turn your lights off every time you leave the room, no matter how short the duration.

(All of the above was cut and pasted from the link below.)

Edit:  The second link below has THIS to say on the subject:

Fluorescent Lighting:

The cost effectiveness of turning fluorescent lights off to conserve energy is a bit more complicated. For most areas of the United States, a general rule-of-thumb for when to turn off a fluorescent light is if you leave a room for more than 15 minutes, it is probably more cost effective to turn the light off. Or in other words, if you leave the room for only up to 15 minutes, it will generally be more cost effective to leave the light(s) on. In areas where electric rates are high and/or during peak demand periods, this period may be as low as 5 minutes.

Fluorescent lights are more expensive to buy, and their operating life is more affected by the number of times they are switched on and off, relative to incandescent lights. Therefore, it is a cost trade-off between saving energy and money by turning a light off "frequently" and having to replace the bulbs "more" frequently. This is because the reduction in usable lamp life due to frequent on/off switching will probably be greater than the benefit of extending the useful life of the bulb from reduced use. By frequent we mean turning the light off and on many times during the day.

It is a popularly held belief that fluorescent lights use a "lot" of energy to get started, and thus it is better not to turn them off for "short" periods. There is an increase in power demand when a light is switched on, and the exact amount of this increase depends on the type of ballast and lamp. The ballast provides an initial high voltage for starting the lamp and regulates the lamp current during operation. There are three basic types of ballasts: magnetic (of which there are energy-efficient and not so energy-efficient types), cathode-disconnect, and electronic. All types can operate two or more lamps simultaneously. There are three main methods that are used in a lamp's ballast to start the lamp: preheat, rapid-start, and instant-start.

Answer 2

It saves electricity turning lights off whet it is not needed.

But frequent turning lights on and off tears light bulbs at a higher grade.

So, if we speak about saving money, it is a question, what comes first.

Answer 3

It does not take "a lot of electricity" to turn a light on -- it uses the same energy as one that's already on.

And, even if it were true that it used more electricity, how much more could it use, versus the percentage of time the light is off versus on?  Suppose you were to keep it on 8 hours a day.  Do you really think it takes the equivalent of 16 hours of electricity to turn it on?

Now, there is some debate, as I understand it, as to the longevity of a typical filament lightbulb, and the wear that turning it on causes.  (Have you ever seen a lightbulb burn out while it's on?  Or only at the instant you turn it on?)  This is, of course, a totally different question.