Relatedly: why is flickering LEDs so common? I presume most people also just don't see/don't care?
Going with lower voltage is less efficient as the LED will output less light per voltage but not linearly, it will still use most of the power of full brightness at half.
Choosing PWM allows you to skip this problem by keeping the voltage identical but by using human persistence of vision to get the ideal number of photons to your eyes per your perception frame. The problem comes from making a slow PWM signal, say 60Hz, or having two similar but not identical PWM signals near each other, such as two different TV screens with a different backlight PWM frequency. That can make you see flashing because of the out of phase brightness peaks and troughs lining up.
The flicker that bothers me, and maybe the GP, is likely due to cost cutting in the LED power supply. Not enough filtering or ability to handle the normal voltage dips in a home electrical system. As above, the solution is usually to spend more $ on bulbs, but not a guarantee.
I have some near ceiling lights that allow dimming via a remote control (infra red or 433MHz) or fast switching on/off (remembering their state afterwards).
There are other ways to communicate, e.g. using the zero cross - the dimmer can send whatever signal to the lights downstream - the latter would read it and set the brightness.
I don't think this is true? Aren't LEDs more efficient at lower voltages/currents?
This is because leds have a fixed voltage drop and just a bit above that your light efficiency is almost zero.
The real reason for PWM dimming is simplicity, expanse and size.
Turning an LED on and off is a lot simpler than a real constant-current LED driver: indicator LEDs can be driven directly from a digital output on a microcontroller, or switched with just a mosfet. Constant current is always going to be more components.
In AC-powered applications, making an LED not flicker at 100/120Hz requires capacitance for energy storage, which are bulky and unreliable.
Strobing can also be dangerous around rotating machinery, like a lathe, because at certain RPM the machine will appear to not be spinning.
I believe the solution is to use a buck converter with enough inductance to ensure that the current to the LED is not interrupted.
Also the PWM can be in the high 30KHz w/o much of switching sacrifice loses, not even dogs would react on it.
I use TP-link Kasa color-changing bulbs (although I'd be happy with any that can change colour temperature between daylight and candlelight), and the flicker sometimes bothers me.
• Cheap lights on a bike? Flicker.
• Lights on an expensive SUV? Flicker.
• Lights at Starbucks or at my library? Flicker.
• My phone (Pixel 5)? Flickers (I use a PWM reducing app that works by applying an overlay).
• Nearly 30% of all lighting at homes/commercial spaces and nearly 100% of those LED Edison bulbs? Flicker.
Maybe you have a "leading edge" dimmer, whereas most LEDs needs trailing edge.