I've had to, actually. But I am curious about the answer, as well, so I did a little research. Supposedly if you use an incandescent bulb with a lower voltage, you make the coefficient of efficiency worse but you simultaneously extend the lifespan of it by quite a bit. In a oven, low energy efficiency is not a major problem as the waste heat just gets to be used in heating the oven itself. So perhaps the lamps are quite usual but just get used at a lower voltage? Or perhaps the filament is thicker so it burns slower. I didn't arrive at an answer, but have few plausible conjectures instead.
Moonside wrote
I've had to, actually. But I am curious about the answer, as well, so I did a little research. Supposedly if you use an incandescent bulb with a lower voltage, you make the coefficient of efficiency worse but you simultaneously extend the lifespan of it by quite a bit. In a oven, low energy efficiency is not a major problem as the waste heat just gets to be used in heating the oven itself. So perhaps the lamps are quite usual but just get used at a lower voltage? Or perhaps the filament is thicker so it burns slower. I didn't arrive at an answer, but have few plausible conjectures instead.