> That means you need to be able to scale your backlight by a factor of 10^10 to cover the whole human vision range.
Uh, phones don't produce brightness that high. And the low range is "too low" for usefulness anyway. Your math is off by few factors
> And if your CPU runs at 1 Ghz (10^9), then at the dimmest setting then even being on for a single clock cycle would be a flash every 10 seconds - clearly unacceptable, and even then, few backlight controllers could handle a 1 nanosecond pulse!
CPU is not doing PWM, it's separate chip
And you can't realistically have more than few kHz of PWM frequency anyway coz of losses.
It's not really a technical problem in the first place, it's easy technically, just have 2 current sources, when you need low light you just PWM the low current one. And not "just putting resistor in series", that's extremely wasteful, or "single led" that would just not illuminate evenly.
Unfortunately at these low currents, you tend to get a tiny amount of leakage across the LED junction - just a few microamps, but trying to make a small amount of light it becomes an issue. Worse, you can't even calibrate for it because the leakage is highly temperature dependant.
Uh, phones don't produce brightness that high. And the low range is "too low" for usefulness anyway. Your math is off by few factors
> And if your CPU runs at 1 Ghz (10^9), then at the dimmest setting then even being on for a single clock cycle would be a flash every 10 seconds - clearly unacceptable, and even then, few backlight controllers could handle a 1 nanosecond pulse!
CPU is not doing PWM, it's separate chip
And you can't realistically have more than few kHz of PWM frequency anyway coz of losses.
It's not really a technical problem in the first place, it's easy technically, just have 2 current sources, when you need low light you just PWM the low current one. And not "just putting resistor in series", that's extremely wasteful, or "single led" that would just not illuminate evenly.