I actually saw that done in one oven (remote LED plus 'light pipe') but I can't remember which make (I suspect one of the 'expensive' ones!)
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Its these modern mat black interiors that make it impossible to see inside without a light. I remember my parents had an oven with light grey enamel with inserts that you could remove for cleaning. Why dont they make the interiors like that now. All this silly self cleaning rubbish that doesn't work. And dont you have to put your oven on 3,000 degrees to "self clean" - how does that get an AAA**** rating.
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I’m moving towards the light!!!
Speaking about lamps/bulbs whatever you wants to call them
Two things come to mind.
Those of you who know me will be aware of one of my little sayings
"The word average is one of the most dangerous words in the universe" Which "Average" are we referencing when we state the word? Arithmetical mean, Geometric Mean, RMS, Median, Mode then allowing for standard deviations and non-standard deviations. Sometimes these figures hover around a similar approximation yet often they do not.
They can be used to advise us of how typical things might be yet they can/are often used to deceive us both intentionally or accidently.
Quite often only an oversight of all this info might give us a reasonable insight for a reasonable approximation.
Therefore "Average" can be good or it can be dangerous!
Traditional filament lamps that we have employed for years had stated average life expectancy.
So far so good (not withstanding what I wrote above) yet how were those averages obtained anyhow?
Often when doing destructive tests to see life expectancy of filament lamps they quoted times on/off (the mark/space ratio) of being several hours at a time, how often do we use filament lamps or any lamp at all in large hourly cycles. We often switched the on for a few mins then off again for a few mins or a few hours. All these short duration switching on and off really stresses filament lamps and throws out of kilter any results, reliable or not, for figure gained by three or four hour constants during test runs.
With oven lamps etc, you also have obscene temperature differences and air flow thrown into the mix.
I would suggest that leaving them on days/weeks/months/years gives the only real expectation of life and gives us a true best figure to work with, the only way we can beat that is to leave them switched off, they last forever then.
This is true of filament lamps and perhaps more so of fluorescents too. LEDs I`m not sure of, they are still "relatively young".
Two things come to mind.
Those of you who know me will be aware of one of my little sayings
"The word average is one of the most dangerous words in the universe" Which "Average" are we referencing when we state the word? Arithmetical mean, Geometric Mean, RMS, Median, Mode then allowing for standard deviations and non-standard deviations. Sometimes these figures hover around a similar approximation yet often they do not.
They can be used to advise us of how typical things might be yet they can/are often used to deceive us both intentionally or accidently.
Quite often only an oversight of all this info might give us a reasonable insight for a reasonable approximation.
Therefore "Average" can be good or it can be dangerous!
Traditional filament lamps that we have employed for years had stated average life expectancy.
So far so good (not withstanding what I wrote above) yet how were those averages obtained anyhow?
Often when doing destructive tests to see life expectancy of filament lamps they quoted times on/off (the mark/space ratio) of being several hours at a time, how often do we use filament lamps or any lamp at all in large hourly cycles. We often switched the on for a few mins then off again for a few mins or a few hours. All these short duration switching on and off really stresses filament lamps and throws out of kilter any results, reliable or not, for figure gained by three or four hour constants during test runs.
With oven lamps etc, you also have obscene temperature differences and air flow thrown into the mix.
I would suggest that leaving them on days/weeks/months/years gives the only real expectation of life and gives us a true best figure to work with, the only way we can beat that is to leave them switched off, they last forever then.
This is true of filament lamps and perhaps more so of fluorescents too. LEDs I`m not sure of, they are still "relatively young".
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All very true. However, since we live in a world in which almost everything (both 'animal' and 'mineral') is subject to some degree of variation (commonly fairly 'random'), we are totally reliant on ;averages' (of whatever sort) as a means of describing/reporting the 'typical' properties of things (dimensions, weight, numbers, life expectancy etc. etc.)
However, as you say, averages can easily be misunderstood/misinterpreted, and are sometimes deliberately used to deceives - and the same is true of 'percentages'.
In some contexts, mean and median 'averages' may be similar - indeed, they will be identical if the pattern of 'failures' (or dimensions, or whatever) is 'symmetrical' around the average. The more 'symmetrical', the greater will be the difference. However, as I've said, the main difference is a practical one - testing to establish a median survival of, say, 1,000 hours need only take a bit over 1,000 hours (about 6months), whereas to determine the mean survival of the same batch of products might take 20 years or more (having to continue until the last item fails).
How means can 'mislead' was brought home to me when, many moons ago, I was researching my family history. We are inclined to believe that average human life expectancy has, in most countries, increased dramatically over the decades and centuries - and that is undoubtedly true in terms of mean life expectancy. However, when doing my research, I noted that they great majority of my ancestors lived for roughly the same amount of time as they do today, most dying between 65 and 85. I also noted that even thousands of years ago, there are Biblical references to human lifespan being "three score years and 10" (70 years).
The explanation, of course, was that there was a very high rate of child mortality, with many babies dying withing days or weeks of birth, and probably less than half surviving to adolescence. This large number of very short life-expectancies dramatically reduced the mean survival - but the median survival has not changed all that much - if the median is, say, 70 years, when those who survive less than 70 years die when they are one day old, then that median will still be 70b years if all those who dies befoore 70 die at, say, 69.
Very much so. It was pretty rare for filament bulbs to fail other than at 'switch on' (when filament was cold and hence low resistance), so testing should obviously seek to reflect the pattern of on/off/on switching in normal service. One cannot really expect them to test under countless different ';usage conditions' (which would probably just confuse users, anyway!)(,so I imagine they use a 'usage pattern' which they believe, rightly or wrongly, is typical of 'common usage' - but maybe they've got that wrong.
I have to say that, at least in my case, although we were probably much more 'careful' (because of 'running costs') in the days of incandescent bulbs, we don't do much 'switching on and off' of lights these days, other than perhaps in loos and bathrooms. Lights in 'living areas' tend to be left on continuously during non-daylight hours, and those in bedrooms just switched on/off once per day.
Indeed. As I've always said, oven lamps/bulbs are a very exceptional case,and one would hope that bulbs designed for this use are tested using something approaching the pattern of real-world use. However, as I've said,I'm not convinced that all lamps/bulbs used in ovens are necessarily designed and manufactured specifically for only that application - in which case some might only be tested under totally inappropriate conditions (for an oven lamp/bulb).
Kind Regards, John
I would assume the life expectancy hours, would be determined by running them on several different over voltages, then from that, extrapolate the likely life on the correct voltage.
I used to urge (in the days of filaments and fluoros ) that folk did not switch if if likely next use was within 20 mins, mainly hallways, stairways and bathrooms in reality
Well, we can 'assume' whatever we like, but I, for one, do not know what they actually do.
In reality, I would suspect that they do whatever produces the most 'optimistic' figure they dare to claim (i.e. whilst remaining such that they could try to justify the basis of their claim if they were challenged).
Any extrapolation from one set of test conditions to some other usage conditions will be little more than guesswork.
There was a time figure oft quoted long ago, for florescent lighting, where it was cheaper to leave them on, than switch off and back on - calculating wear and tear, plus the extra current drawn at start up.
Obviously some interpretation is involved, but overloading is a common way to be able to determine safe working loads for many things.
Any reduction in the number of 'switch-ons' is almost bound to increase life expectancy (of a filament lamp/bulb), so one obviously had to balance the cost of earlier replacement (plus a little 'inconvenience') against the increased running costs (particularly with incandescents) of switching them off less often. Different people obviously suggested different 'rules-of-thumb' which attempt to achieve that.
A filament cools rapidly (hence its resistance reduces rapidly) after switch-off, so switching back on at any time beyond a minute or two after switch-off will probably have the same impact on life expectancy.
Kind Regards, John
Methods of 'accelerated testing' are attempted in most fields, to reduce the time that it takes to get an estimate of 'life expectancy' (it's even used for 'stability testing' to get estimates of 'shelf-life' for medicines) - but, as I said, extrapolation from that to real-world ('non-accelerated') usage can never be much more than guesswork.
In the case of medicines, although accelerated tests are used to define (usually very conservatively) the 'shelf-life'; to be stated initially (and hence to minimise delays in the medicine becoming available for use), but non-accelerated testing (i.e. under 'normal in-service conditions') is usually started at the same time, so that it eventually becomes possible to revise (if necessary) the shelf-life which was estimated y 'extrapolation' from 'abnormal' conditions.
We saw something like this with the Pfizer Covid vaccine. Initially, the required storage conditions were very demanding, resulting in logistical problems of transport, deployment and utilisation (sometimes resulting in some vaccine having to be thrown away). However, when results of the 'real world conditions' stability tests became available, it was possible to considerably relax the requirements.
My 20 min suggestion was to reduce the number of switching cycles without putting them off by suggesting far more than 20 mins which was more likely to encourage the advice to be completely ignored.
even so, the conspiracy theorists had a field day by suggesting proper testing was not do as it was historically and added to their graphine, microchip/G5 theories . They "Proved" then it was a con or to harm folk, yer can`t win with some folks. Anyway it all helps to get proper considered logic out of the window and politics/religion/hocus pocus out into mainstream .
A pity really because it detracts by making folks less likely to believe some cases of "hang on, are we getting this right here?" questions actually side lined when perhaps we actually should be taking heed,
I realise that but, as I said, any off-period of more than a minute or two would have the same impact on life expectancy, so the balance of 'the equation' is almost entirely driven by the running cost of having the light on when not needed.
Incandescent bulbs were very cheap- let's say 40p each 'back then', with an expected life of about a year - so an expected replacement cost of about 40p per year. If one left the light on when not needed such as to double (rather optimistic!) the life to two years, the saving in bulb replacement costs would be 20p per year. However, even at electricity prices back then, it would not have taken many 20-minuteperiods of having the light on 'unnecessarily' for the running costs of that extra usage to exceed that 20pper year saving!
Kind Regards, John
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