After years of use, the 4 lamps in the oven needed replacement. Ibought some from a local shop which were marked 230v and they lasted just weeks, got another set from ebay listed as 220 - 240v which each lasted only a week. all were marked as oven lamps, but I wasn't conviced about that, due to the glass being very clear, rather than toughened. Very annoying, because they are not that easy to change.
Latest set have lasted a month and were 2 for a pound from Poundland, marked 240v on the package and on the lamp base, the glass was also discoulored suggesting they were toughened. Better yet, they have lasted a month so far ;-)
Try explaining to numpty sales people that 220v is very different from the 240v in the UK :'(
There are no exceptions to the requirement. Filament lamps should be designed to work at 253V, even if that means there is a slight loss of light output at 216V.
The difference in light output between those to voltages is quite considerable. In the days when the UK had various mains voltages, you could buy lamps of 210, 220, 230, 240 and I think 250v ratings.
even 50v which one of the Cambridge colleges had in 1960 - the town having a 200v supply. It was soldring irons that suffered really badly if you had a 240v element on 200v.
25v and 50V are still common as working lights on machine tools, although modern ones tend to use 12V H1 halogen lamps, presumably as they are readily available for cars.
We used to have a wide variety of different voltage lamps in the Electricity Museum. DC systems were often 100V or 110V, but could be used to charge lead acid batteries in houses, with house voltages anywhere between 12V and 96V. There were also traction lamps, for use on trains at track voltages in the range 500-630V DC.
However, while early lamps were made to exactly match the supply voltages, a necessity with the poor quality of early filaments, latterly, if you looked closely at the markings on the lamps, one that was sold for 220V could be exactly the same as one sold for 240V. People were so used to buying lamps to match their supply that it was simpler to put the same lamp in different packages than to try to educate them to the fact that you could run a 240V rated lamp on 220V, but not necessarily the reverse.
After WW2 before Dad settled down he worked with an electrician in a rural area. We ended up with a large box of SBC lamps of various voltages rendered redundant by the coming of std AC mains replacing home generators . Too tempting for a youngster so experimentation was undertaken. Some lamps just shattered others had a short but brilliant career.
24V was found to take out the circuit fuse but the filament remained intact. Adding a 0 with a chinagraph pencil and replacing one of the lamps in a school corridor ensured the caretaker would go from his usaul mild mannered self to a swearing purple coloured monster over an hour or so. Some of the 200V+ lamps were coloured so for years the outside loo was bathed brightly in green/red, orange and blue as the lamps were used up.
Certainly a consideration. But even rough service mains lamps have a short life when subjected to vibration. So even on a tool where lubricant wouldn't normally be used any built in lights are better if low voltage.
I'm afraid to say this, but that last paragraph is basically a load of bullshit. Regardless of 'poor quality of early filaments' the design criteria is still affected by the same physical laws that determine the life versus luminous efficacy trade offs made with today's high quality filaments.
The improved quality of filament just allows for an improved luminous efficacy for a given lamp life (1000 hours being the standard lamp life arrived at all those years ago as offering the best TCO between the electricity and lamp replacement costs).
Once you've decided what the lamp life should be, the voltage is pretty well determined within 1 or 2 percent for a given wattage and lamp life.
Tungsten filament GLS lamps are very sensitive to voltage variations that can readily be dismissed by most other domestic appliances.
For voltage variations within +/-25% of nominal, each 5% increase will approximate to a halving of lamp life (and associated improvement of efficacy). Conversely, a 5% reduction will double the lamp life and reduce efficacy.
220v is just slightly shy of a 5% reduction on 'our harmonised 230v mains' and similarly, 240v is just shy of a 5% increase. It should be blindingly obvious why tungsten filament GLS lamps have _always_ been marked with a singular votage rating to this day.
A tungsten filament GLS lamp designed for the notional harmonised voltage of 230 cannot be sold in the UK and on the continent where most supplies are using the 220v level since a lamp that lasts 2000 hours on the continent will only last 500 hours in the UK. We'd find ourselves replacing lamps four times as frequently as our continental neighbours.
There's a very good reason why lamps sold in the uk with 240v printed on the envelope are _really_ 240v filamented lamps (and similarly in the case of 220v lamps sold in most of continental Europe).
Modern electronically ballasted fluorescent lamps (both linear and CFLs) and mains voltage LED lamps can be readily designed to cope with such variations so can be sold with 220-240v voltage ratings. The good old fashoined tungsten filament GLS lamp however, still has to work within the constraints of 'Physical laws'.
I would pass that on to the curator of the Electricity Museum, who showed me the markings and explained the situation, but he was a retiree when I was in my 20s and he is now long gone.
That was not my experience at all - On say a 210v supply, in an awkward to get to location, it was common to deliberately install say a 240v lamp, to increase the life. It would be noticeably dimmer for a comparable lamp of the correct voltage. Fit a 210 lamp, in a 240v situation then you would be replacing it very soon.
The difference between the correct lamp for the voltage was not only noticeable by its life, but by its brightness.
Local shops, would stock the local voltage, but for another voltage it involved atrip to the wholesalers.
230v is a politician's description rather than a real physical one. UK still has a 240v target voltage, and France etc 220v. What has changed is a) what the voltages are called b) appliance specs, which are now specced - where possible - to cope with both supplies. c) and the outer limits of what's permitted for supplies, which is of small significance in practice.
FWIW 1000 hours is not minimum TCO for GLS, but I expect it was when the standard was decided. US uses 750 hours, which is closer. Long life lamps are even further from minimum TCO, and even more so when overpriced.
IIRC the last significant change was the coiled coil, introduced in the 1930s. If you buy vanilla GLS you're getting 1930s technology.
There have been other developments since, but either very minor (higher temp rated cement enabling smaller envelopes) or large enough to produce new lamp types, halogen & xenon.
That's exactly why ordinary tungsten filament GLS lamps have to have their voltage so closely matched to the mains supply voltage local to the regions they're sold in.
The "Thousand Hour" lamp life does have its origins in the early days. My reference for this figure comes from the "Lamps and Lighting" (second edition) published in 1972, reprinted 1979. This must have been when lamps cost relatively more compared to the unit price of electricity than is the case today.
I suspect the reason for sticking with the 1000 hour rating was more to do with satisfying established expectations by the general public in the matter of 'lamp quality'.
The yanks seem to have really gone overboard in the matter of rejigging the lamp life hour rating down to a mere 750 when you consider that the lower voltage filaments will straight away offer a superior TCO compared to 220 and 240 volt filaments even at the 1000 hour life rating.
There's a very good reason why 12v halogen downlighters have such endurance when powered via a modern current limiting electronic ballast compared to their cheap 'n' cheerful 240v counterparts.
The wikipedia article on tungsten lamps, whilst pretty good, is a bit skimpy on the detail (but still worth a look if you want to check your basic facts). Particulary informative in this case, is the link to "lamp rerating" that can be found there towards the end of the article.
That's certainly the case with our Bosch double oven which we acquired (2nd hand but hardly used) just two and half years ago.
Only one of the E14 40W Philips 300 deg C rated lamps was bought new at the time, the other being an original lamp. Neither have needed to be replaced so far but it's only the top smaller grille/oven that's seen regular use and I can't undo the jamjar bottom pyrex glass cover to take a closer look at the lamp itself without using some sort of 'Jar Lid Opening Tool' to get the extra purchase and leverage to examine that lamp to see whether it was it was the new or the old lamp.
Even when trying to undo the more accessible lamp glass in the lower oven, I found it a bit of a struggle but I was able to verify that the lamp rating was indeed a full 40W, as well as testing that the totally ubiquitous 15W E14 300 deg C oven lamp (2 for a quid) would fit and at least relieve the darkness of the oven's interior recesses 'in a pinch'.
At somewhere in the region of a fiver a pop for the Bosch 40W oven lamp, I'll happily make do with the standard 15W Pygmy oven lamp thank you very much. I think the only reason I 'splashed the cash' in this case was on account we needed a replacement jamjar bottom pyrex glass lamp cover anyway so I added the 'special lamp' to the order.
The thing is with oven lamps, they have to be rated for for an ambient temperature of 300 deg C as well as for the mains voltage in use. Even if the standard glass envelope is still ok at that temperature the filament could well land up running a good 200 deg C higher than designed for if an ordinary lamp 'dressed up as mutton, so to speak' were to be used.
Even a 15W pygmy oven lamp needs to specified precisely for the mains supply voltage in use by the oven. In the UK, it should specify 240v, definitely not 220-240v which makes me suspicious straight away as to whether it would actually be rated for 300 deg C ambient.
Where are you buying your oven lamps from? Does your oven use the readily (and only) available 15W E14 Pygmy oven lamp, or is it something a little more inconveniently exotic like the ones used in our Bosch oven?
They came from an ebay seller, listed as 240v oven lamps by the seller,
6 for £5 6 months ago and standard 15w E14.
When they turned up, they were marked 220-240v and a month later, they had all 6 blown. Since when, it did without any lamps until recently. None of the 2 for a £1 Poundland lamps have failed yet, which suggests they are the pukka item.
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