When the Lights Go Out - Page 1
Forum section: electronics / general

author: olsenn
author_rank: Frequent Contributor
timestamp: September 07, 2013, 07:02:05 pm
content: This one is kind of confusing me. Why is it that light bulbs rarely break during the time that they're on, and instead tend to break the moment you first turn it on? Is it a quick change in temperature or something that causes the filament to go?

author: PA0PBZ
author_rank: Super Contributor
timestamp: September 07, 2013, 07:18:03 pm
content: I think a cold filament has a lower resistance, so the current will peak when you switch it on.

author: Monkeh
author_rank: Super Contributor
timestamp: September 07, 2013, 07:20:12 pm
content: Quote from: olsenn on September 07, 2013, 07:02:05 pmPrecisely. They behave exactly like a fuse.

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 07, 2013, 07:22:44 pm
content: If you're still using those old fashioned bulbs, install dimmers to soft start them. Or just swap them for good quality fluorescents/LEDs.

author: Lightages
author_rank: Unknown
timestamp: September 07, 2013, 07:25:01 pm
content: It is because as tungsten filaments glow for a long time they evaporate away over time. Eventually there is not enough material left to support the turn on shock caused by the inductive kick. The filaments are coil wound like springs. As the current kicks in the filament does a little jump from the magnetic field it induces and it can withstand this until the filament gets sufficiently thin that it can no longer mechanically support this movement and it breaks.When the filament is hot and you turn it off it is running at high resistance and is fairly pliable and therefore can withstand the inductive kick as the magnetic field collapses.It will also depend on when you actually turn on the switch whether the you are connecting the circuit at the zero crossover of the AC waveform or at one of the peaks. At zero crossover the inductive kick is less than switching on at peak value.

author: Rufus
author_rank: Super Contributor
timestamp: September 07, 2013, 08:59:35 pm
content: Quote from: NiHaoMike on September 07, 2013, 07:22:44 pmSoft starting makes little difference - it doesn't reduce wear on a good filament just slightly delays the death of a worn out one.Quote from: Lightages on September 07, 2013, 07:25:01 pmI doubt there is anything inductive about it. Filaments neck down because thin parts run hotter and evaporate faster. On turn on the neck gets hot faster because it has less thermal mass and being thinner more resistance and more resistance again because it is getting hotter. At some point the neck will just melt before the rest of the filament warms up.

author: IanB
author_rank: Super Contributor
timestamp: September 07, 2013, 09:40:30 pm
content: Quote from: Rufus on September 07, 2013, 08:59:35 pmEvery light in my house is on a dimmer switch and I usually run them at 1/3 to 1/2 brightness, which is all that's needed for moving about the house. They typically last for years without failure due to the low stress on the filament. The only time I need a full brightness lamp is for reading or close up detail work.The long life mainly comes from running at low power, but I'm sure the soft start helps too by limiting the cold start current rush.This is also why CFLs are a failure. They can't be dimmed, and I would be blinded by a full brightness lamp.

author: Kjelt
author_rank: Super Contributor
timestamp: September 07, 2013, 09:45:25 pm
content: Quote from: IanB on September 07, 2013, 09:40:30 pmCan't speak about the US but in Europe there are many CFL's in the market that can be dimmed. Problem with dimming CFL's is that the color temperature rises instead of dropping like an old fashioned lightbulb, so the light becomes white/blueér instead of cosy warm yellow. So LED is now the way to go, they even now put yellow led's in some bulbs to emulate the original old fashioned light bulb.

author: IanB
author_rank: Super Contributor
timestamp: September 07, 2013, 09:55:39 pm
content: Pretty much every CFL in the USA has "not dimmable" on the packaging. To make them dimmable would require even more complex and wasteful electronics inside the lamp* and would increase the cost of manufacture. In the US market the retail buying decision for almost anything is "How much is it? Is it cheap? Can it be cheaper? That's too expensive!" You cannot add a feature to anything without decimating your sales volume.* And this is another reason why CFLs are so bad. Every lamp contains a complex electronic circuit that wastes some rare earth minerals each time the lamp is disposed of after its sadly short working life. Not to mention all the pollution caused by the factories in China that make the billions of lamps required.

author: rdl
author_rank: Super Contributor
timestamp: September 07, 2013, 10:15:45 pm
content: I just picked up a couple of LED "bulbs" last week, and from what I can see, this is probably the future of home lighting. I can't tell the difference from regular incandescent bulbs as far as color. If you want pure white or daylight color temperature, you can get them. The manufacturers claim they will last over 10 years. They run very cool. If you touch them after they've been on for hours they're barely warm.One is made by Cree and the other is from Philips. The 800 lumen 60 watt equivalent Cree uses just 9.5 watts. The Philips 136 lumen uses 3 watts and is going in a lamp that burns out a regular 15 watt bulb about every 3-4 months for some reason. I paid $8 for it, so if it lasts just a year it will have paid for itself easily. The Cree was $12, probably won't break even on it for a year or so. I expect there's still room for the price to come down a bit more.

author: Psi
author_rank: Super Contributor
timestamp: September 08, 2013, 12:30:34 am
content: You used to be able to buy 250V lightbulbs (instead of 230V).I'm not sure what they were intended for but people who lived right next to the 11kV transformer used them because they would last much longer than a regular 230V lamp. (Due to the transformer output being quite a bit higher than 230V for houses right next to it).I think they've pretty much fixed all that now using more transformers and shorter runs.

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 08, 2013, 01:05:57 am
content: Quote from: IanB on September 07, 2013, 09:55:39 pmWhat's wrong with linear fluorescents? They're used extensively in offices and the overall reliability is very hard to match.I also read about an incandescent (or halogen) bulb that has a built in diode so it could use a shorter but thicker filament for the same wattage.

author: olsenn
author_rank: Frequent Contributor
timestamp: September 08, 2013, 01:08:54 am
content: So here's a question: if the cause of most bulbs busting is a surge of current to an already weak filaments, could slowly ramping up the current each time it's turned on make the bulb last a few more years?

author: IanB
author_rank: Super Contributor
timestamp: September 08, 2013, 01:13:17 am
content: Quote from: olsenn on September 08, 2013, 01:08:54 amI think so. Soft start is almost a requirement for very large lamps.

author: Rufus
author_rank: Super Contributor
timestamp: September 08, 2013, 01:56:32 am
content: Quote from: wilfred on September 08, 2013, 01:29:57 amMaking incandescent lamps last 'for ever' is easy. Halve the voltage you get about 1/8th the light output and they last about 8000 times longer.For domestic applications where lamps are cheap and easily replaced they should be designed for around 1-2000 hours life. Otherwise you spend more on energy supplying a low efficiency long life lamp than you would replacing a higher efficiency lamp every 1-2000 hours.

author: Psi
author_rank: Super Contributor
timestamp: September 08, 2013, 02:45:58 am
content: Quote from: wilfred on September 08, 2013, 01:29:57 amdamn, that must suck.Do you find other things fail as well? (other than lamps)

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 08, 2013, 04:33:11 am
content: Quote from: Psi on September 08, 2013, 02:45:58 amEasy fix is to install dimmers on all the incandescent lights (optionally "calibrating" them with a true RMS meter) or replace those with quality fluorescent or LED. Electronic stuff designed for 240V shouldn't mind it and motors would actually start easier.

author: SeanB
author_rank: Super Contributor
timestamp: September 08, 2013, 10:27:16 am
content: These work well, and are pretty long lasting.http://www.lighting-gallery.net/gallery/displayimage.php?pid=9721&fullsize=1Made pre war, still going strong.

author: David_AVD
author_rank: Super Contributor
timestamp: September 08, 2013, 12:09:06 pm
content: Soft starting incandescent lamps definitely does increase their working life. Running them slightly dimmed does too. We have dimmers on most lamps at home and they last for a long long time.Fluorescent lamps are great for office and workshop use, but they are butt ugly for home use. The only ones we have at home are in the garage.Dimmable LED lamps are becoming more common and slowly dropping in price. I've tried a few and am just waiting for them to get a bit better and cheaper before replacing the dicroic lamps.LED replacements for linear fluorescent tubes are not at a viable price / performance point yet imo.

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 08, 2013, 01:18:10 pm
content: Quote from: David_AVD on September 08, 2013, 12:09:06 pmThey make fixtures that cover the bulbs. There are also circular bulbs (not CFLs) that fit in more "traditional" lamp styles.

author: Bloch
author_rank: Unknown
timestamp: September 08, 2013, 01:55:28 pm
content: Quote from: SeanB on September 08, 2013, 10:27:16 amYes apparently very easy to make lamps last for a very long time !That to domake then break before timehttp://topdocumentaryfilms.com/light-bulb-conspiracy/

author: Legit-Design
author_rank: Frequent Contributor
timestamp: September 08, 2013, 04:00:19 pm
content: Quote from: Bloch on September 08, 2013, 01:55:28 pmLike in everything there are trade-offs. As can be seen on that picture lightbulb barely glows. If we actually had lightbulbs like that, which seem to last forever, people would complain that they are wasting power and not providing sufficient lighting. So people would probably buy lights from manufacturer which provides more light and break more easily.Similar thing with modern CFL-bulbs, they could last longer but manufacturing would probably cost more, people wouldn't buy them because they cost so much.Nothing is stopping people from putting up their own light bulb/whatever manufacturing, it could be funded by crowdfunding. Make sure to provide all the necessary info on how long the bulbs will last what the manufacturing costs are, how much will you need to get profit from each bulb to make it viable.

author: SeanB
author_rank: Super Contributor
timestamp: September 08, 2013, 04:55:18 pm
content: Reason for the dim glow is it was dimmed, so the camera could make an image of the filament without washing out totally from the light. It is actually a reasonably bright lamp otherwise, not too bright to read by, but perfect as a close up reading light. 32 candle power was certainly bright enough for most purposes.

author: David_AVD
author_rank: Super Contributor
timestamp: September 08, 2013, 09:10:57 pm
content: Quote from: NiHaoMike on September 08, 2013, 01:18:10 pmI still find the light output of fluorescent tubes objectionable for home use. Warm white LEDs are the closest to incandescent that I do like.

author: c4757p
author_rank: Super Contributor
timestamp: September 08, 2013, 09:19:01 pm
content: Am I the only one whopreferscool fluorescent lighting to incandescent? It just looks kind of weird to me when everything is lit up in yellow light. Fluorescent lamps are closer to daylight.

author: rexxar
author_rank: Frequent Contributor
timestamp: September 08, 2013, 10:23:15 pm
content: Quote from: c4757p on September 08, 2013, 09:19:01 pmNo, I rather like cool light. My ceiling fixtures all had incandescents in them when we moved in, and everything looks all yellow and washed out. I'll probably replace them with LEDs when the bulbs finally die.

author: IanB
author_rank: Super Contributor
timestamp: September 08, 2013, 10:31:35 pm
content: Quote from: c4757p on September 08, 2013, 09:19:01 pmI don't know, but count me out. I really like the warm yellow light of dimmed incandescent bulbs. It's reminiscent of firelight. I think it's restful on the eyes because the light has an even coverage of the whole spectrum like sunlight. I find fluorescent and LED lighting to be very tiring. I just look at a fluorescent light and think, "ugh, why is it a funny color?"(Also, I think there is no difference in light quality between fluorescent and LED lights. They each use fluorescent dyes in various mixtures to produce visible light.)

author: c4757p
author_rank: Super Contributor
timestamp: September 08, 2013, 10:33:07 pm
content: Quote from: IanB on September 08, 2013, 10:31:35 pmAgreed, they look identical.

author: ElectroIrradiator
author_rank: Frequent Contributor
timestamp: September 08, 2013, 10:44:03 pm
content: Quote from: c4757p on September 08, 2013, 09:19:01 pmI prefer anything, which emits a continuous spectrum. Something both fluorescent and LED lightbulbs have a hard time replicating. I will probably move to daylight balanced Xenon lamps soon-ish (not getting younger here, need ever more candle power for working on small items).

author: steve30
author_rank: Frequent Contributor
timestamp: September 09, 2013, 02:09:17 pm
content: Quote from: c4757p on September 08, 2013, 09:19:01 pmc4757p: I like daylight fluorescent lamps. For the last year, in my combined bedroom/lab I've been using Osram Lumilux De Luxe tubes (CRI >90, 5400k). They do the job pretty well. I have blue carpet and blue walls, and anything under 5000k makes the blue colours look like a muddy yellow. Even my 4000k tubes do that. 4000k looks nice in other areas though.I do quite like tungsten lamps, especially if one wants a small 'cosy' light. In fact, my small desk lamp has a Philips halogen lamp which was replaced about 13 years ago and is still working well after many, many hours of use.Main issue I have with conventional 'light bulbs' is glare, which I why I switched to fluorescent tubes round the side of the room. I do have some nice daylight CFLs (6000k) (from Androv Medical), but don't use them in here any more because of the glare.