electricity

[doorknob]

Does switching your lights on and off use more electricity than leaving them on?  Does it depend on the length of time left on?  or vary with the type of light (flourescent, normal or "green")?

Are there any figures anywhere to back up an answer (my wife won't believe you otherwise).

[Skids]

Flourescent tubes draw more current when illluminating than they do to stay illuminated.  Ordinary and "green" bulbs have the same current draw all the time they are on.  The problem with most "green" bulbs is the warm up time they take to acheive full luminosity.  Ordinary bulbs should be switched off whenever they are not needed.  Whether you want to switch off flourescent or "green" bulbs depends on how frequently you're going in and out of the room.  What ever you do it has very little effect on your electricity bill (unless you leave them on all the time).

[greenday]

In addition, the more you turn light on and off the more likely it is that the filament will blow. So turning of may save money, but do it too much and you will end replacing more bulbs, thus costing you more.

[brachiopod]

It is always better to turn an ordinary tungsten (filament) light on and off as required. I'm not sure about shortening the bulb's life, but even if it does (drastically) it's still cheaper to turn it off. Here's some figures for your missus, doorknob!

I have a 100W bulb in my bathroom. In order to prevent shortening the bulbs life, in the evening I leave it on for 5 1/2 (5.5) hours, rather than switching on and off for the 1/2 hour that I actually need it.
This is using a net 5 hours a day of electricity more than I would otherwise require, at a cost of;
0.1 x 5 x 7 x 8.0 = 28p per week
('Power' rating in KWh x no.of hours x 7 days x cost of unit of electricity in pence)

I can get a three pack of 100W bulbs from my local Wilkinson for �1.29 - a cost of 43p each.

Even if, by constantly switching the bulb on and off, I shorten the bulb's life to two weeks, it will cost me less to replace it, than to preserve it's life by needlessly leaving it on for 5 hours every day.
(43p to replace it every fortnight v. 56p to leave it on an extra 5 hours a day)

 

I don't have any figures for this, but I remember doing some calculation for fluorescent lighting when I was at school (>20 yrs ago !). The results were that if the lighting would be required again within something like 20-30 minutes, it was not worth switching them off, as it would require more electricity to re-start than to leave them on.

[landie]

Not an answer, but where does the light go when it's switched off?

[QmunkE]

The photons bounce around and are absorbed or just reflect out of the room at the speed of light, and are dissipated into the universe.

[Bert]

I was so happy to see brachiopod emphasising the correct spelling of fluorescent.  Just say the word slowly, doorknob and skids, "flu-or-es-cent" and you too will be able to spell it.