A dim but enough to read by and handsfree red light is also good for my (occasional) astronomy. I'm still looking for the right light for that.
Is there a frequency at which the pwm ceases to be hard work for the eyes?
IEEE1789 makes some reasonable recommendations for frequency and modulation. For 100% modulation, they suggest the switching frequency should be above 1250Hz. That seems about right for my own experience of LED flicker: I can see artefacts on fast-moving objects at 1kHz, but it's not otherwise noticeable. (I can see 100Hz flicker quite easily, but it doesn't usually bother me.) But I don't think IEEE1789 goes far enough for the minority of people who are particularly sensitive, or when movement is to be expected (eg. vehicle lighting).
In our informal tests, barakta can see the flicker up to about 6kHz. I doubt she's unique, though the effect on her visual system is extremely unusual (most people who are sensitive will suffer migraine, fatigue or autistic over-stimulation without necessarily being aware of the cause of the problem
[1], rather than see stroboscopic artefacts on non-moving objects). On that basis, I'd want it above 10kHz for a decent safety margin, at which point you're bang in the middle of the audio range, which is a recipe for sensory assault by whistling inductors instead. (Also interference with audio-frequency electronic equipment, such as recording devices, guitar pickups or hearing aid induction loops.)
We have a couple of desk lamps that switch in the ~50kHz range. Neither of us can tell the difference between that and DC, even with fast-moving objects.
I'd suggest that if you're driving LEDs with PWM, the frequency should be above the audio band, in the tens of kilohertz. DC current-dimming (which can still be done using efficient switching regulators) may be appropriate if low-end colour stability isn't critical. Anything with more than a slight ripple
[2] at AC mains frequency belongs in the bin. I expect the IEEE and lighting organisations will come around to this view eventually, with the no-name Chinese manufacturers catching up several decades later.
[1] I bet some of the 'allergic to WiFi' brigade are in this category.
[2] Impressively, barakta can see the 100Hz ripple on halogen lighting, so even that's not immune.