The simple reason is that it's not a light bulb, it's a heater.
They are running it at much lower than specified voltage, so are generating mostly heat, and almost no light, so the filament is not very hot. It's glowing a dull red, not white.
There is a quadratic relationship between temperature; and efficiency plus bulb life.
You may have heard of the phoebus cartel - they specified a specific bulb life, which directly translates into a particular energy efficiency. There's nothing about the manufacture of the bulb that they casued to be worse, rather if the bulb lasts too long, you just up the temperature and make a more efficient bulb (uses less electricity).
You can buy stage bulbs that last barely 10 hours, and run extremely hot, and also efficient, and for film that is the tradeoff they prefer (I guess they need a lot of light, and they don't really keep bulbs for long).
They are running it at much lower than specified voltage, so are generating mostly heat, and almost no light, so the filament is not very hot. It's glowing a dull red, not white.
There is a quadratic relationship between temperature; and efficiency plus bulb life.
You may have heard of the phoebus cartel - they specified a specific bulb life, which directly translates into a particular energy efficiency. There's nothing about the manufacture of the bulb that they casued to be worse, rather if the bulb lasts too long, you just up the temperature and make a more efficient bulb (uses less electricity).
You can buy stage bulbs that last barely 10 hours, and run extremely hot, and also efficient, and for film that is the tradeoff they prefer (I guess they need a lot of light, and they don't really keep bulbs for long).