CFLs - switching on and off

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On Sat, 18 Aug 2007 10:40:33 -0700, snipped-for-privacy@hotmail.com wrote:

Why do you say they don't mind? Haven't you noticed that they almost always burn out at the moment they are turned on?
That's when they heat up, the filament expands (maybe faster than when it contracts on turning it off) and stresses on the filament are greatest.
If you leave a filament bulb on, it will generally last much longer than if you turn it on and off.

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On or about Sun, 19 Aug 2007 04:07:06 -0400 did mm

I was amazed no one had pointed out the error in that statement, and was about to comment. Sure enough, last message in the thread, and I'm scooped.
--
- Mike

Ignore the Python in me to send e-mail.
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Most incandescents do not suffer significant wear from starting. What happens is that an aging filament becomes unable to survive a cold start a little before it becomes unable to survive continuous operation.
An incandescent burnout is generally from melting of a thiner hotter section of the filament. Such a "thin spot" has a temperature overshoot during a cold start.
Once a filament has a hot-running thin spot that becaomes unable to survive a cold start, its hours are numbered. The thin spot suffers worse evaporation because it runs hotter, and this condition accelerates worse than exponentially, so the filament's days/hours are numbered once it is in bad enough shape to be unable to survive a cold start.
- Don Klipstein ( snipped-for-privacy@misty.com)
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mm wrote:

Do you have further information on this? I understood that avoidance of switch-on surges gave only minimal extra life to GLS lamps, though considerable extra life to halogens.
NT
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We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember snipped-for-privacy@care2.com saying something like:

As anecdotal evidence only... I've noticed (as have others) that side-mounted filament lamps don't last long, typically a few months of normal useage. Since powering a desktop lamp through a push-button dimmer and using that dimmer as the only on/off switch the same bulb has been in that lamp for the past 4 years. Ordinary 60W bulb, btw.
--

Dave

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Curmudgeon wrote:

Many dimmers don't let you achieve full brightness. The bulb may randomly have longer-than-average life. Some "ordinary" bulbs are long-life versions (with slightly less light output).
So I am not surprised.
- Don Klipstein ( snipped-for-privacy@misty.com)
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We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember snipped-for-privacy@manx.misty.com (Don Klipstein) saying something like:

Good for you. Have a coconut.
--

Dave

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On Sun, 19 Aug 2007 08:34:27 -0700 someone who may be snipped-for-privacy@care2.com wrote this:-

It is the same with valves. Left on they can last for a very long time, turned on and off they can be unreliable. See Tommy Flowers, 1930s telecommunications equipment and the genesis of Colossus for the evidence.
--
David Hansen, Edinburgh
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David Hansen wrote:

But the 2 situations arent comparable afaics. Filament failure vs oxdide contamination on a filament heater running only red hot.
NT
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On Mon, 20 Aug 2007 11:38:55 -0700 someone who may be snipped-for-privacy@care2.com wrote this:-

The comparison is one of whether leaving on equipment involving hot bits of metal has advantages in terms of reliability. It does in many fields, but this has to be weighed against the energy consumption of doing so.
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David Hansen, Edinburgh
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wrote:

During the time it is energised the filament loses metal and gets thinner, not necessarily uniformly along it's length. Eg. It is cooled where it is supported and less metal is lost at these points.
Where it is thinnest is also where it is mechanically weak and it's electrical resistance is greatest. At switch on the whole filament has a low resistance and takes a big surge of current. The thin weak points are heated up disproportionately to the rest of the filament and eventually the filament will fail at one of these points.
I don't think that routine switching on and off shortens the life of the lamp that much, but rather that a lamp at the end of it's life which has become frail will tend to fail when it's switched on.
DG
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Not good for filament lamps too. In fact, too many switching operations are not good for most things like computers, motors, TVs, etc. Switching transients (both switching on and off) could have many thousand volts and could draw 10x or more rated current across the device which could results in electrical, mechanical and thermo shock. Note many lamp failures are at the moment of switching either on or off.
My own experience is CFLs (and Circle Lines) are much more susceptible to switching than incandescent or the 4' and 8' fluorescent lamps. YMMV.

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on 8/19/2007 12:17 PM ** Frank ** said the following:

Yes, MMDV (no, not 2505. My Mileage Did Vary) I've had the spiral CFL bulbs installed in all of my formerly incandescent bulb lamps, wherever the lamp took a regular bulb. The exceptions are mini spots, and decorative candelabra bulbs. The CFLs in my basement stair lights have been operated for the past 4 years, and at least 4X a day, and more. The others have been changed over the past couple of years None have not failed yet. They only take a few seconds to full brightness, and when first turned on, they are about 80% bright. They are GE, if that makes a difference.

--

Bill
In Hamptonburgh, NY
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On Sun, 19 Aug 2007 12:55:17 -0400 someone who may be willshak

There are now some good energy saving bulbs for these.

While there is no equivalent of clear bulbs there are now a number of "candle" shaped energy saving bulbs that are very similar to pearl "candle" bulbs.
It is becoming difficult to find an indoor application where there is not a suitable energy saving bulb.
--
David Hansen, Edinburgh
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Many thanks for all your informative and illuminating inputs - the way ahead is much brighter now. I amazed that this thread has not degenerated into the usual flaming after a few posts - I can only assume that a better class of person inhabits the a.h.r and uk.diy threads. Best regards.
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snipped-for-privacy@hotmail.com wrote:

Perhaps if we'd been discussing gas lamps it might have done...
NT
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David Hansen wrote:

CFL candle lamps will fit chandeliers etc, but imho they dont come anywhere near being a replacement in visual terms. The appearance is bulkier, ungainly, and they have no sparkle at all, unlike clear filament candles. Also with chandeliers the splitting of colours depends on a small light source, so use of CFLs does this no favours either. Chandeliers are one app where filaments still rule. LV filaments can at least gain a bit more efficiency over mains.
NT
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Actually, regular mains filament lamps don't care about switching, and it doesn't shorten their lives. (This might not apply to high current and halogen lamps, for which I haven't seen figures.)

That's why people think that switching shortens their life, but it's a misunderstanding of what's happening. At the end of life, lamps can continue operating for a few hours past the point where they won't survive another switch-on. If you switch them off during this period, they will blow at next switch-on, and in the case of a lamp which isn't normally switched on for an hour or more, it's pretty certain to blow at a switchon rather than whilst running. However, this is independant of the number of times the lamp has been switched on in the past and depends only on burning hours. There are a number of applications where this effect can be measured, such as continuously flashing signs which use regular lamps, where life can be seen to depend on total burning hours and not frequency of switching.

Assuming the most common fluorescent tube failure mode (electrode emission mix all sputtered off), it depends on the design of the control gear, and not much on the type of tube.
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Andrew Gabriel
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