... but why is the retinal persistance, on which multiplexing relies, so short with LED's when it is essentially 33 ms in a TV? After all, the TV displays one pixel at a time with a 33 ms frame rate.

Can you elucidate? Is there a reason? How does ambient lighting affect this?

Yes, it does, but, in TV, it's quite short relative to the retinal persistence. That's why some people are acutely aware of the inherent "flicker" while most don't see it at all. This was particularly painful when video games that used interlace became popular. I'd guess Erik Malund knows more than most of us about this effect with LED's.

I'm trying to get Erik Malund to tell us what he knows about LED's of this type. After all, he works with this technology all the time.

The type of LED's with which I originally worked took microseconds, or at least the major part of a microsecond to "light up" and didn't "light up" fully for several microseconds. Further, their behavior was not in any sense linear with current or voltage

Todays LEDs turn on and off very fast, my shortest PWM pulse is ~30uS
Because of that and the Human retina you need to do EVERYTHING affecting light on/off in less that 8ms for everybody, 10ms for most and 15ms for a few or you will have complaints about flicker.
if you do not have the full on/off cyscle done in 8ms some will se flicker.
How does ambient lighting affect this ambient light does affect this becuse ir requires you to vary the on time.

Erik

an anecdote:
when I designed my first color sign I said to myself "TV refreshes at 50Hz (60 in the US), let me make that my goal, the result was HORRIBLE flicker.