I heard this when I was younger and have always wondered if it was true. Someone told me something like "it takes more energy to turn a light on than it does to run it for 2 hours, so if you are going to turn it on again in a few minutes it's better to leave it on.
Does the act of turning an appliance or light on take more energy than running it for x amount of time?
- Thread starter KingGheedora
- Start date
I've never heard that before, but I really have no idea... I can't imagine how that's possibly true.
Mythbusters addressed this. It only saves electricity if you leave the light on for less than a tenth of a second (or less, depending on the type of bulb).
DainBramaged
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Capt Caveman
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RocksteadyDotNet
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It's more true for devices with capacitors.
And fridges. Starting a fridge motor takes alot more current than it uses once it's running.
Incandescent light bulbs behave like a short circuit for a brief instant when they are turned on, then increase in resistance rapidly. In that transient period, they will draw more current than they will at steady-state. However, the difference is not nearly enough to make your 2 hour figure work. The Mythbusters did indeed address this.
Other devices will be different, but again the difference in energy usage is unlikely to approach the kind of level you are talking about.
In general, the larger concern (and IIRC, one ignored by the Mythbusters episode) is the wear caused when a device is cycled frequently. All else being equal, an incandescent bulb that is turned on for a minute at a time every several minutes will not last nearly as long as one that is turned on and left alone. This again varies quite a bit depending on the kind of device you are looking at.
Other devices will be different, but again the difference in energy usage is unlikely to approach the kind of level you are talking about.
In general, the larger concern (and IIRC, one ignored by the Mythbusters episode) is the wear caused when a device is cycled frequently. All else being equal, an incandescent bulb that is turned on for a minute at a time every several minutes will not last nearly as long as one that is turned on and left alone. This again varies quite a bit depending on the kind of device you are looking at.
Jeff7
Lifer
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Yes, it takes more energy to turn on something than it uses in X amount of time.
X just tends to be fairly small.
A CFL with an instant start ballast uses a short burst of several hundred volts at startup to ionize the gas. At what amperage, I don't know, but I'd wager that the wattage used is higher than the tube's normal consumption. But it does it for a very short time, so "x amount of time" is very short. The concern with CFLs is that the startup stresses the tube, so it's not a good idea to use fluorescent lights where they're only going to be on for a few minutes with each use. The same holds true with regular long tube-type fluorescents. I don't know if I've got these numbers right, but this is the gist of it:
Philips Alto tubes are rated 24000 hours at 3 hours on-time per start, and 30000 hours at 12 hours on-time per start on an instant start ballast.
This increases by about 6000 hours with a programmed start ballast.
A TV or computer monitor will have a degaussing coil go off at startup. This does use a lot of power, but again, it's only for a very short time.
Stuff with compressors: The startup current draw is very high, and can come close to reaching the limit of a standard circuit breaker. But it's brief. So let's say you get 15A draw at 120V for a full 5 seconds. 2.5 watt-hours from startup. Again, "x amount of time" is going to be very brief.
X just tends to be fairly small.
A CFL with an instant start ballast uses a short burst of several hundred volts at startup to ionize the gas. At what amperage, I don't know, but I'd wager that the wattage used is higher than the tube's normal consumption. But it does it for a very short time, so "x amount of time" is very short. The concern with CFLs is that the startup stresses the tube, so it's not a good idea to use fluorescent lights where they're only going to be on for a few minutes with each use. The same holds true with regular long tube-type fluorescents. I don't know if I've got these numbers right, but this is the gist of it:
Philips Alto tubes are rated 24000 hours at 3 hours on-time per start, and 30000 hours at 12 hours on-time per start on an instant start ballast.
This increases by about 6000 hours with a programmed start ballast.
A TV or computer monitor will have a degaussing coil go off at startup. This does use a lot of power, but again, it's only for a very short time.
Stuff with compressors: The startup current draw is very high, and can come close to reaching the limit of a standard circuit breaker. But it's brief. So let's say you get 15A draw at 120V for a full 5 seconds. 2.5 watt-hours from startup. Again, "x amount of time" is going to be very brief.
I think so. When you turn on the power the electricity flows through the coils without any back EMF, no, until the motor gets up to speed?
Seems to happen with Laptops. I get more *time* leaving it running for the battery length, than rebooting it 4 or 5 times during one charge. Rebooting seems to take on average 3-5% of the battery life.
Jeff7
Lifer
- Jan 4, 2001
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Not too surprising. During bootup, the hard drive is going crazy, and there's probably a decent level of CPU usage as well. Most of your time spent using the laptop is likely just on ATOT, or maybe typing up something in Word, neither of which stresses the computer much.
Add in (with modern laptops at least) downclocking of the CPU/voltage reduction, and GPU (be it integrated or discrete) which doesn't happen during the boot process (when everything is running at full power, before the drivers kick in)
Originally posted by: Jeff7
Yes, it takes more energy to turn on something than it uses in X amount of time.
X just tends to be fairly small.
A CFL with an instant start ballast uses a short burst of several hundred volts at startup to ionize the gas. At what amperage, I don't know, but I'd wager that the wattage used is higher than the tube's normal consumption. But it does it for a very short time, so "x amount of time" is very short. The concern with CFLs is that the startup stresses the tube, so it's not a good idea to use fluorescent lights where they're only going to be on for a few minutes with each use. The same holds true with regular long tube-type fluorescents. I don't know if I've got these numbers right, but this is the gist of it:
Philips Alto tubes are rated 24000 hours at 3 hours on-time per start, and 30000 hours at 12 hours on-time per start on an instant start ballast.
This increases by about 6000 hours with a programmed start ballast.
A TV or computer monitor will have a degaussing coil go off at startup. This does use a lot of power, but again, it's only for a very short time.
Stuff with compressors: The startup current draw is very high, and can come close to reaching the limit of a standard circuit breaker. But it's brief. So let's say you get 15A draw at 120V for a full 5 seconds. 2.5 watt-hours from startup. Again, "x amount of time" is going to be very brief.
what about lcd's?
i step away from the computer long enough for it to energy save and power off. is it better off leaving it on?
it's set to 30 mins.
nakedfrog
No Lifer
- Apr 3, 2001
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Nope, they addressed that too, they put the bulbs on an automatic switch.
Scroll down towards the end
Jeff7
Lifer
- Jan 4, 2001
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An LCD uses CCFL tubes for backlighting. I don't know anything about the electronics with them. I think they use high-frequency, high-voltage AC to light those up, but that could be way off. I don't know what the startup cycle looks like, or how harsh it is on the tubes.
I can't imagine that the screen itself would suffer from any ill effects.
Not entirely true.
The reason it is better to leave a HVAC/AC/heater left on set at a certain temp is because when it kicks on it has to stay on longer to reach that set temp. So a significant amount of time is just GETTING to the right temp. Maintaining it doesn't require the same amount of energy.
My cousin's daughter was born deaf, so her whole family quickly learned sign language. When her second daughter was born, she quickly learned it too. It was really cute to see four- and five-year-old girls signing to each other.
I don't know that it's cool, but it certainly can be helpful in the right situation. Many toddlers can communicate with sign language long before they can use their words. So, if you want to play guessing games for 6-12months, skip it, otherwise teaching them a few signs for Eat, Drink, and a few of their favorite things can be a real benefit. Actually, it is pretty cool--you'd have to like kids and be a parent though to appreciate it, I guess.
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