Polite way to ride in the dark
Consider how you feel when a fellow cyclist approaches you will full beam straight ahead. It's pretty blinding, even for a moment, and especially off-road when your eyes aren't used to it.

So in a park:


Dim your light to its lowest setting (within reason).
Put it on steady beam. Flashing is more visible but also more annoying and
disorientating.
Physically push it forwards/downwards so it's pointing towards the ground, not into anyone's face.


If you do this then it doesn't matter whether you illuminate pedestrians or for how long.