Electricity usage question. What is more energy efficient?

I remember being told when I was a kid that leaving a light bulb on is more energy efficient than turning it off and on, if you are only leaving a room for a few minutes.

I have always been one to turn off lights, or the TV (or any electrical appliance) if I leave a room, unless I know I will be coming right back. But I’ve always wondered about this.

When you turn on a light (or a TV, etc) is there a slight uptick in electricity that surges through the wires to light the bulb when its off? In my experience, light bulbs only die at the moment I turn on a switch; they never burn out if they are currently on. I thought the power draw was increased at the moment the electrical circuit is completed to turn whatever on.

I would guess that a bulb can die if you leave it on indefinitely, however I once read that the longest bulb in continuous usage has been on since it was screwed in, and that was when bulbs first came out (if I remember correctly, the bulb was in a 24-hour facility, like a fire station or police station, and the light is never turned off.)

Anyone know? And if there is a benefit to leaving the lights on vs. turning them off if you leave a room for a short time, whst is the over/under on time? Is it 5 minutes? Or does it depend on the wattage and other factors?

Here’s an SD column, there are also a number of previous threads - short answer is, turn them off.

every electrical device has a finite lifetime in some number of hours. there is an average number for that device (model, year, version) which you might be above or below. for many devices they no longer last as long as they used to.

turn on is often a bit of a knock to the device. many devices also have a number on ‘turn on’ that it can take; you might be above or below the average. there is a balance of turn on times verses running hours; you might know in general what it might be for that type of device but there is no specific predicting.

that long burning light bulb is also running at a much lower voltage than it was designed for or is useful. it is being babied for lifetime.

a CFL bulb is best left on for 30 minutes or longer (i.e. turn on stress them a bit). so i use some other light if needed for a short time.

for an incandescent bulb i would leave it on if i would be turning it on again in the next 15 or 20 minutes, if planned and not hundreds of watts.

LED bulbs are really good for turning on and off as needed.

Thanks for the links.

Cecil covered it in 1980. I’m a bit late to the party.

There is a surge of current when you turn on a light. For incadescent globes, this surge is short enought so that you should never leave a light on “to save power”.

For flourescent (tube) globes, the surge is big enough so that flicking the light on and off wastes more power than just leaving it on, but if you are going to be out of the room longer than the time it takes for the light to warm up and turn on, you should turn it off.

For modern flourescents that turn on almost immediately, the same rule applies: the time after you turn it on, before it lights up, is wasted. If it takes half a second to turn on, then you are wasting power if you leave it on for more than half a second when you are out of the room.

I don’t always turn all lights out: I consider if it will be more convenient for me to have the light turned on. But I’m not saving power if I walk through a door without turning off the light: I’m just saving aggravation.

This is only true if you consider the immediate usage of power. But turning a fluorescent on causes a small amount of erosion of its electrodes. Too frequent of power cycling will cause them to burn out much sooner than they are expected. Taking into account the energy used to make the tubes means you should leave them on unless you’re going to be out of the room for a long time. The 30 minutes someone suggested above is probably minimal. I don’t shut mine off unless I’ll be gone for over 3 hours.

I have a ‘thing’ about turning stull off. It comes from a period when I was really poor and had to feed coins in a slot to get power.

My computer power bar turns off when I turn the comp off - so that’s the sound and the printer too. The plugs for the TV etc have remote radio controlled switches and go off when we go to bed (unless there is an OTA update due). Lights are on and off as needed - LED is great for that - I used to get to the fridge before the kitchen fluorescent flickered into like, now it is instant.

Keeping something on will ALWAYS use more power than turning it off and turning it on again when you need it later. That goes for all kinds of lights, heating, air conditioning, everything. (Well, ok, not aluminium factories.)

However, there are a few things that will age faster if you turn them off/on more often, especially things that get pretty hot such as incandescent lights. But it’s still not worth it to worry about this in normal use. Just turn off stuff you don’t use and save a little energy.

Aside on that long-lived light bulb:

That would be the Centennial Light of the Livermore-Pleasanton Fire Department, which has been lit nearly continuously since 1901. It has been out briefly a few times because the Livermore Fire Department moved a few times, taking the bulb with it; also, the occasional power outage.

It is now world-famous, and being babied indeed. It lives it its own carefully pressurized and climate-controlled enclosure, with its own special low-voltage power supply (which itself went out once), and its own dedicated webcam.

Excerpt from Wikipedia:

My university told us that 10 minutes was too short. And that was 30 years ago. And the replacement policy for large buildings meant that failed globes waste a lot more energy than you would have where the tubes were easy to replace. 3 hours is just excessive.

Thanks for posting this link.

I am always amazed (and a bit surprised) when I recall some little nugget like the light bulb being in a fire house, and finding out that I was correct. The human brain is an amazing thing, and I am fascinated that some strange, obscure nugget like that was not only hiding out in my grey matter, but I was able to recall it when needed.

Of course, I rarely remember where I put my car keys, but I’ll take what I can get.

Ah yes, Straight Dope as Dear Abby

I remember this from the mid-60’s.

Next up: Toilet Paper: Does the end hang next to the wall or away from it?

No, nor for any practical meaning of “leaving it on”.

The cost is in the purchase price of the bulb, the surge current decreases the life by some hours… (on average…), and so then each turn off/on costs so much life, so the cost of an off/on cycle is (wasted lifetime/total lifetime) * purchase price
Thats going to be small …They do survive many turns on and off, they don’t survive being overheated…