What happens if you use a non-dimmable LED on a dimmer?

Obviously you should not do this, but if someone did it, what would
happen? Would the LED simply not light unless the dimmer was on FULL
brightness, or would the LED (or maybe the dimmer) be damaged?

Just curious!

And while we're on this topic, I know that photocells often begin to
turn on a light at less than full brightness, based on the amount of
natural light at dusk. So, I'm assuming those fixtures require a
dimmable LED. correct?