220-240v lamps

[Nightjar]

On 21/03/2014 19:29, Harry Bloomfield wrote: ...

Hint: It was a museum.

Colin Bignell

[Bob Henson]

You did get ones that were specifically marked as oven lamps for 300°C use? Like :-

There are similar ones that are not temperature rated and presumably won't last very long.

[Johny B Good]

Ah, that's good news then (selfishly thinking of me with my 'poundland' spares). Well, at least you know where to get the next set of replacements from (if you ever need any more, that is!).

[meow2222]

life/LIFE = (VOLTS/volts)^13 & efficacy/EFFICACY = (volts/VOLTS)^1.9

I assume it dates back to the 1930s or earlier. Back then people used to repair tungsten lamps. The 30s was the era of (illegal?) price fixing for lamps. Then again electricity was eyewateringly expensive too at 5p a unit.

750 gets you better TCO. OTOH no-one appreciates short lamp life.

also has ways to increase lamp life or efficacy.

NT

[meow2222]

The 300C rating is the standard, but unnecessary. You have a lamp enclosure with upto 220C one side, 20-40C the other, so the rise in operating temp i s 100-110C. This does push filament temp up, but that's of minor consequenc e given how little ovens are used. The big difference is the cement in the bulb base, which is definitely not rated for the temp rise. You thus get a higher failure rate there, with glass parting from base sometimes. Some app liance lamps also have hardened glass to resist shattering into food, I for get whether that includes oven rated lamps. In practice though theyre behin d a glass cover.

NT

[Harry Bloomfield]

Yes I did!

[Andrew Gabriel]

TCO also includes the relamping costs.

Streetlamps (back in the days of filament ones) usually used double life and sometimes triple life lamps, because a) The relamping costs were high, and b) They paid a rate which worked out typically only 1/4 of the standard domestic electricity rate.

There's no one right value.

[Andrew Gabriel]

That's not true.

There have been deployments of better gas fills, which reduce filament evaporation, and reduce heat loss by convection cooling of the filament.

Tungsten Halogen lamp.

Move to low voltage filament lamps (more efficient).

Infra-red reflective coatings to reflect the IR emission back onto the filament.

Most recently, there has been the development of tungsten filament surfaces with an interference pattern to prevent emission of IR wavelengths. (This has been demonstrated, but abandoned due to many countries banning filament lamps, rather than banning lamps below certain efficiences).

Coiled-coil is just to get around that 240V is a long way from the most efficient filament lamp voltage for lamps below a few hundred watts - it needs the filament to be so thin it has too much surface area, which the coiled-coil counteracts to some extent. (The most efficient design voltage for 100W filament lamp is about 55V.)

Oven lamps are heavily under-run. If yours have short life, it's for some other reason - vibration of a fan or slamming the oven door, stress on the lamp, overheating, etc.

[Windmill]

If that's correct, it tells us something about the true cost of generating electricity. While they might sell it at cost for such purposes, I doubt they'd sell it at a loss.

[Andrew Gabriel]

There was a surpless at night, which was also the driver for economy 7 and similar dual rate tarrifs - to try and use up the power generated by plant which can't wind up and down as quickly as once a day.