I just don't understand why all movie set lights haven't instantly been replaced by their LED equivalent. Why do people still use these things that are crazy expensive to run and can set things on fire?
The situation can also be flipped and apply to light sources, and those by definition are key in photography.
In case of LED light, its colour balance can be declared to match some reference Kelvin number, but because it is “fake”, a mix of spikes in the spectrum (roughly at R, G, and B for RGB LEDs, phosphorus-covered white LEDs have the spectrum more even but its own gaps and bumps), and materials of various colours can reflect inbetween those peaks, or right at those peaks, those materials can look 1) different from scene to scene and from light to light or 2) plain wrong in post production, compounding variance between camera sensors or films (which create colour from their own mix of R, G, and B), lenses, etc.
Added to other flaws of LEDs, such as longevity (of cheaper units), issues with brightness and colour reproduction consistency, PWM, etc., they make a poor choice for a variety of situations[0], but in photography particularly so, particularly where colour reproduction and continuity matter (TV and film).
By contrast, black body radiation—hot and more energy intensive—is a solid spectrum of even light, without spectral discontinuities or flicker at any brightness.
[0] In some situations those flaws are considered acceptable. You may have noticed how two identical OLED iPhones displayed at an Apple Store, even fully reset to defaults, can have obviously different white point when you look at them side by side—that’s colour reproduction/emission variance and/or degradation over time. Similarly, you can often spot PWM flicker if you reduce brightness and squint at an OLED phone with your peripheral vision. These things don’t matter much, since 99.99% of the time we look only at our own device and our colour perception and flicker tolerance is adjusted to it. Not so with photography; you can’t afford colour variance between two different lights even in cases where it’s not noticeable to the naked eye in the moment, whereas PWM restricts your FPS and shutter angle options.
Take a CD / DVD (if you can find one in 2023) and look at the spectrum from your phone flash, or any other LED lamp, and observe the broad spectrum. They all have some sort of blue peak, but it's very small in "warm white" lights.
Other issues, such as PWM flicker coinciding with your FPS and shutter angle or LED controller interference in audio recording, remain.
From my understanding, today mature LED-based solutions can only mitigate these issues with varying success, not eliminate all of them entirely, all this mitigation adding complexity and cost, while on the other hand one could just use a black body emitter so that those issues are not technically a thing, and try not to set things on fire.
That said, if you need a lot of light, halogen is without alternative. There's a reason the ArriMAX with its 18kW halogen lamp is still popular.
I believe they still use PWM to dim, and you still need to work around the flicker by choosing the right frequency depending on your FPS and shutter angle. They help by making PWM frequency configurable but that is mitigating the problem not eliminating it.
Some directors prefer the spectrum completeness and profile from tungsten (or the ultimate, carbon-arc, which is virtually indistinguishable from the sun.)
I also think there are levels of light that aren't really feasible except with carbon arc because LEDs don't like heat and that limits power density.
I don't remember what movie it was, but there's a photo of an enormous balloon light - larger than an entire house - over a farmhouse somewhere in the midwest, at night. Pretty sure it wasn't LEDs as the source, but I could be wrong.
Not a balloon, but a big diffuser with a whole bunch of Cineo 410 LED sources.