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Old 11th Jun 2019, 10:37 pm   #61
emeritus
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Default Re: The lightbulb conspiracy

Getting back to the alleged "conspiracy" theme, I just dug out my GEC 1911 lighting catalogue. Something I hadn't noticed before is a series of graphs of light output versus time for "Robertson" carbon filament lamps. The "Life" axis ends at 800 hours, and seems to reflect the then-current British Standard. The graphs show that, at the 800 hour point, light output was still in excess of the British Standard end of life criterion. I know from another contemporary book about Robertson lamps that Robertson defined the end of life with reference to the "Smashing point", being the point at which the lamp had blackened so much that the light output was no longer adequate, and not the point at which the filament failed.

No corresponding information was supplied for their Tungsten lamps. Possibly as they were new technology at the time, a British Standard hadn't yet been established.

Regarding series operation of low wattage lamps, it appears that this was an absolute necessity at the time because it was not possible to manufacture Tungsten wire thin enough to make satisfactory low wattage bulbs for 200-250V operation. Striplight fittings for shops that took small or candle bulbs were available with multiple lampholders connected either in series for 200V operation or parallel for 25V to 120V operation. While "Robertson" tubular striplight Carbon lamps were available for up to 200-250V operation, "Osram" Tungsten tubular striplight lamps were only available for 25V.

GEC also supplied transformers and autotransformers for operating low voltage lamps from 200- 250V mains supplies, 50 Hz as standard, 25 to 100Hz to special order.

Lamps intended for series burning could be supplied in matched pairs.
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Old 12th Jun 2019, 8:38 pm   #62
Restoration73
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Default Re: The lightbulb conspiracy

"Inefficient" tungsten lamps provided a secondary source of heat, and probably saved
a few from hypothermia death. I found this book interesting ;

https://www.deathofalightbulb.com/
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Old 13th Jun 2019, 10:18 am   #63
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Default Re: The lightbulb conspiracy

There is a factor that affects life that doesn't directly impact on the light output. That is the inert gas used in the bulb.

This is something that car manufacturers are very well aware of. Decades ago your brake lights often needed replacing, but not these days. I can't remember the last time I had a car bulb fail.

So what changed? The answer is warranty length. When manufacturers competed to offer long warranties - when manufacturing had improved enough to make this feasible - the life of the lights started to become the main reason for warranty claims. The main dealers charged a huge lot to change a bulb, billing the manufacturer, so they changed from cheap argon to more expensive krypton and xenon.
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Old 13th Jun 2019, 11:07 am   #64
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Default Re: The lightbulb conspiracy

Interesting. The gas or vacuum surrounding the filament is important - a minute amount of water vapour plays havoc with life, as per the water cycle. But given that water is eliminated effectively, what is the benefit on using dry krypton or xenon rather than dry argon? These are all inert gases.
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Old 13th Jun 2019, 11:49 am   #65
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Default Re: The lightbulb conspiracy

Filling a bulb with Krypton or Xenon instead of the cheaper Argon, can be used to either run the filament hotter and produce more light for the same energy, or alternatively the filament temperature and therefore the output can be left unaltered and the lamp life increased instead.

Vehicle manufacturers have chosen the second option of increased life in order to reduce warranty claims.

Krypton or Xenon filling is also popular for the better quality torch bulbs, generally to obtain more light from the limited and very expensive energy in batteries, rather than to extend the life.

There is no gain from gas filling very low current bulbs but it is worthwhile at higher operating currents.
Note that it is lamp current, not watts, that determines if gas filling is worthwhile.
A 12 volt 21 watt vehicle bulb will be gas filled but a 240 volt 25 watt bulb will usually be vacuum filled.

To determine if a working bulb is gas filled, or vacuum, light it and observe the temperature of the glass. A gas filled bulb will be hotter above the filament whereas a vacuum bulb will be equally hot above or below the filament.

A well used gas filled bulb will be blackened above the filament, a vacuum bulb more evenly blackened.

Vacuum bulbs are preferred for decorative use if exposed to the weather, being equally warm all over they withstand rain or snow better than gas filled bulbs with a hot spot over the filament.
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Old 13th Jun 2019, 3:03 pm   #66
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Default Re: The lightbulb conspiracy

And let's not forget the inclusion of a Halogen in the 'gas' in the bulb - the combination and recombination of the filament material with this produces metal-halides which are redeposited on the filament prolonging its life - but only at high temperatures, which require a Quartz-glass envelope.

https://en.wikipedia.org/wiki/Haloge...#Halogen_cycle

(Hence the "Quartz Halogen" or "Quartz Iodine" headlamps of old, - and the likes of the GU10 spotlamps found in pretty much every kitchen for the last 25 years.)
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Old 14th Jun 2019, 12:19 am   #67
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Default Re: The lightbulb conspiracy

Quote:
Originally Posted by emeritus View Post
Regarding series operation of low wattage lamps, it appears that this was an absolute necessity at the time because it was not possible to manufacture Tungsten wire thin enough to make satisfactory low wattage bulbs for 200-250V operation.
Could it have been that they could make the wire thin enough, but not long enough since they ran out of space to support it properly? I've read somewhere that this was the reason to come up with the double helix filament.
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Old 14th Jun 2019, 1:10 pm   #68
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Default Re: The lightbulb conspiracy

Reading posts #63 to 66, I am reminded of the well-known effect of filament migration experienced with tungsten filaments operating on D.C. supplies in a vacuum, where tungsten filament particles migrate to the + end of the incandescent filament. I wonder, does halogen suppress this action?
Also BTW, I remember some company often advertising in the Daily Express in the early fifties(?) a "Long life" light bulb with a rating of, I think, 100w, with a claimed life of 2000 hours.
They probably sold well, as the ads ran for several years, as I recall. Tony.
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Old Yesterday, 1:12 pm   #69
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Default Re: The lightbulb conspiracy

Just been into one of my boxes of bulbs and came across this. The logo is difficult to read, let alone photograph, but it says "Royal Ediswan, 230v 25w", followed by the crest, then "By appointment to the late King George V Patented. I'm assuming that this means that the bulb would have been made during the period of national mourning after the death of the King, so 1936. The lit photograph is taken with the bulb powered at 60v from a Variac.
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Old Yesterday, 2:20 pm   #70
emeritus
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Default Re: The lightbulb conspiracy

Just dug out another of the old books I rescued from the skip at GEC [ Incandescent Electric Lamps and their properties, Daniel H Ogley, Longman, 1914], which seems to provide the answer to the low voltage, low wattage bulb issue. Chapter VI discusses lamp construction, Chapter VII lamp properties.

In 1910, tungsten filament would have been produced by the "pressed filament" process, which was incapable of producing really fine filaments. By 1914, technology had moved on, and filaments could be produced by drawing tungsten that had been made ductile by heating and hammering while hot prior to drawing. So by 1914, it was possible to make wire less than 0.012mm diameter, allowing the manufacture of 10CP lamps for operation in excess of 200V. (Ch VI, page 50).

Chapter VII discusses life tests and reliability, and indicates that a 1000 hr life had been adopted for metal filament lamps, determined by filament failure rather than light output reduction due to blackening. Page 58 mentions the need to maximise the ratio between light output versus the costs of the lamp and electricity.

Further confirmation, if any were needed, that the alleged conspiracy simply reflects the usual situation in engineering where the optimum solution is one where nothing is perfect, but is a balance between conflicting parameters.

PDFs of Chapter VI and part of Chapter VII attached.
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Old Yesterday, 2:28 pm   #71
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Default Re: The lightbulb conspiracy

I always thought the coiled coil bulb filaments were developed as a way to reduce heat-losses from the filament so it ran hotter and hence gave a "whiter" light.

(Some of the early lightbulbs had a really noticeable yellow tinge to their light)

Hmmm... the filaments of indirectly-heated valves are generally made using a tightly-coiled wire element a length of which is folded back on itself a few times before being fitted into the cathode-tube. I guess that's the only way to get a long-enough piece of filament (high enough resistance) in there.
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Old Today, 5:49 pm   #72
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Default Re: The lightbulb conspiracy

Quote:
Originally Posted by G6Tanuki View Post
I always thought the coiled coil bulb filaments were developed as a way to reduce heat-losses from the filament so it ran hotter and hence gave a "whiter" light.
Your statement above seems to be borne out here: http://www.lamptech.co.uk/Documents/IN%20Coiling.htm
I seem to remember Crompton Lamps having an ad campaign (?1950s) based on the advatages of the coiled coil, although, In retrospect, I suppose most other manufactrers were using the technique as well. They just didn't shout about it though. Tony.
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