CFLs - switching on and off

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

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.

AIUI this old advice was based on an elementary error, as it overloooked the fact that although the tubes may last more hours if left on, they will in fact last less days.

This whole subject is filled with myth and bad advice. Today for domestic installs, the only sensible thing to do is turn off when not wanted, however long or short that may be.

NT

I've just had a Pro-life 25W spiral bulb fail in a spectacular way (very loud bang followed by lingering burnt smell). It's been fitted approximately 6 months.

Photos

There are a lot of "fools" about that believe anything they are told/hear and lack any sort of understanding to know its rubbish. Just look at Lenny in uk.t.b and you will know what I mean.

I bet there are loads of people about that think you should leave the CH on at night as it takes more energy to warm the house up in the morning than it does to keep it warm.. another common misconception doing the rounds.. again!!

I turn mine on and off and they last years (how long I don't know as they are still going after a few years now). What does it prove?.. only that a sample of one or two is meaningless.

Don is a lighting expert with a very informative and detailed site last time I looked. However readers should bear in mind that tube types, starting types, costs, common practices and terminology are all different here in UK to the US.

Also I think somehting was missed in your calculations of switch off break even time. If keeping the tube on for 20 minutes gains you 20 minutes extra tube life, you have in fact gained absolutely nothing. The only difference is that 20 minutes of electricity have been wasted. You wont get a single extra day of service time out of the tube this way. I dont know why but this is so often overlooked in these calculations.

NT

Well, Duh! His obvious point was that if you look at the real facts, which he clearly presented, then it makes no sense, because the current required in the few secs of startup would be huge. And I think your definition of "makes no sense" equals "can't discern intended meaning" isn't exactly mainstream. For example, if someone said that Mars revolves aroung the Earth, the meaning is quite clear, yet any reasonable person would say that makes no sense.

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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

How does that contradict what he said? And it is the issue, like he says below.

They said the same thing about lncandescent lights, btw, and I believed it until I thought about it. My line of thinking was. If turning the light on was equivalent to using 10 minutes of electricity, imagine the time it takes for the bulb to get to full brightness and imagine running 10 minutes worth of electricity through the filament in less than a second. That's a half amp or so times

I haven't read the url below, so I'll leave that for later.

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.

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

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.

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.

I accept that the claim has been made - I have heard people making it as well.

I also expect that is is a corruption of the original research that was looking at overall costs including lamp life and not just running costs. It has just that much of the detail has been lost in the Chinese whispers along the way and it has been reduced to an absurdity concerning just energy costs.

Unless you have one of those pesky CFLs that take 10 mins to achieve a worthwhile light output! ;-)

Nah, don't have that problem...they *never* achieve a worthwhile light output!

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,

On Sun, 19 Aug 2007 12:55:17 -0400 someone who may be willshak wrote this:-

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.

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)