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Alternative oven interior lamps?
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Whales:
I bought some cheap replacements from eBay a while back, but they blew within a month or so.

I suspect that "microwave oven" and "oven" types might be having their terminology blurred by sellers.
thermistor-guy:

--- Quote from: Halcyon on February 23, 2020, 03:29:44 am ---My oven has three halogen interior lights, they are just the small two-pin "push in" type (12 volt from memory).

I'm having to replace them every 2-6 months (presumably because they just get too hot). All that sits between the bulbs and the oven cavity is a plate of glass.

Is anyone aware of better quality bulbs that might be able to stand up to the hot conditions and last longer? Alternatively, is there such a thing as an LED replacement for this application?

--- End quote ---

What brand of bulbs are you using? They might be Chinesium specials, designed to fail quickly.

My oven uses an incandescent lamp, which has lasted for many years. Recently a service tech replaced the lamp, and I had a look at it before he installed it: Smeg brand, made in Italy, still in production, rated at 300 deg. C (from memory).

Oven lamps are exempt from legislation that phase out inefficient lamps with low lm/W, like incandescents and halogens, for practicality. These lamps are still in production.

The filament temperature is critical. As a practical matter, for long life, you want as low a colour temperature as you can get.

Aircraft incandescent lamps rated at 2E5 hours operate at 2000 Kelvin filament temperature. At 2000 K, tungsten has a vapor pressure that is just measurable - in other words, it's just starting to evaporate. Above 2000K, the evaporation increases dramatically.

Another other wear-out mechanism is grain recrystallization. As the filament heats and cools, its grain boundaries reform, and start aligning with each other (instead of interlocking). This makes the filament more fragile - more likely to break because of thermal or mechanical shock. To reduce this effect, long life filaments use Rhenium tungsten which has a higher recrystallization temperature. But these are more expensive - another reason to avoid Chinese "bargains" and go with a geniune spare part from a decent brand.

http://www.tlt.co.jp/tlt/english/products/industrial_light/miniature_lamp/catalog/info.htm

So, TL;DR: go for a decent brand and low colour temperature.
tooki:

--- Quote from: Halcyon on February 23, 2020, 03:29:44 am ---Is anyone aware of better quality bulbs that might be able to stand up to the hot conditions and last longer? Alternatively, is there such a thing as an LED replacement for this application?

--- End quote ---
You realize the only reason we have moved away from incandescent bulbs for general illumination is because they waste 90+% of their energy as heat? And you realize that in an oven, that makes an incandescent bulb essentially 100% efficient? Using ANYTHING else makes zero sense.


I do agree with everyone that you must make sure you're using bulbs specifically sold as oven bulbs. Ordinary ones will not stand up to the oven environment. DO NOT run halogen bulbs below their rated voltage, as jogri said. (It's OK to do so part-time, but they need full-wattage operation at least some of the time.)



--- Quote from: Red Squirrel on February 23, 2020, 06:17:09 pm ---That got me thinking, wonder what IS the alternative?  Surely they are going to stop making incandescent bulbs soon, if they haven’t already.

--- End quote ---
Incandescent is only banned for general lighting. They remain fully legal for decorative and specialty applications.
Halogen is a more efficient subtype of incandescent, and is subject to different regulation, which is why they're still widely permissible.

This isn't going to change any time soon.



--- Quote from: thermistor-guy on February 24, 2020, 01:39:58 am ---The filament temperature is critical. As a practical matter, for long life, you want as low a colour temperature as you can get.

Aircraft incandescent lamps rated at 2E5 hours operate at 2000 Kelvin filament temperature. At 2000 K, tungsten has a vapor pressure that is just measurable - in other words, it's just starting to evaporate. Above 2000K, the evaporation increases dramatically.
--- End quote ---
Except that this applies only to regular incandescent bulbs, and not to halogen bulbs. They are designed to run at higher temperatures and will fail sooner if they aren't allowed to run properly hot long enough. Since the OP's oven uses a halogen bulb, going for a lower color temp is not advisable. (Not that I recall ever seeing different color temp variants of halogen bulbs. Incandescent yes, but not halogen.)
thermistor-guy:

--- Quote from: tooki on February 24, 2020, 04:45:48 am ---...


--- Quote from: thermistor-guy on February 24, 2020, 01:39:58 am ---The filament temperature is critical. As a practical matter, for long life, you want as low a colour temperature as you can get.

Aircraft incandescent lamps rated at 2E5 hours operate at 2000 Kelvin filament temperature. At 2000 K, tungsten has a vapor pressure that is just measurable - in other words, it's just starting to evaporate. Above 2000K, the evaporation increases dramatically.
--- End quote ---
Except that this applies only to regular incandescent bulbs, and not to halogen bulbs. They are designed to run at higher temperatures and will fail sooner if they aren't allowed to run properly hot long enough. Since the OP's oven uses a halogen bulb, going for a lower color temp is not advisable. (Not that I recall ever seeing different color temp variants of halogen bulbs. Incandescent yes, but not halogen.)

--- End quote ---

No, it applies to both. Going for a lower colour temperature (strictly, lower filament temperature) is still advisable if you have the choice. Halogens generally run hotter simply because they are designed to be brighter (to a human observer). The filament needs to be hot enough to dissociate the tungsten halide, but the dissociation temperature depends on the halogen fill gas - it can be below 2000 K, in which case you don't need a filament much hotter than 2000K, thereby promoting a long lamp life.
james_s:
Halogen lamps do indeed fail more quickly if you run them too low. I remember back when those halogen torchier lamps were popular I often saw people leave them on dim for extended periods and the whole "bulb" would turn black in as little as a few hours. You'll probably extend the life if you drop the voltage slightly but if you go down too far it will get shorter. The bulb wall *must* reach sufficient temperature for the halogen cycle to work. The most common cause of short bulb life is cheaply made low quality bulbs. Next is probably a tie between excessive vibration and excessive voltage.

There's really no alternative to incandescent for a high temperature application like that except for maybe HID, but that comes with its own set of problems.
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