What should be the PWM Frequency LED dimming in street light luminary
The term you need to search on is Flicker Fusion Threshold 
Quoting from part of the wiki article, we have this: 


  In some cases, it is possible to see flicker at rates beyond 2 kHz in
  the case of high-speed eye movements (saccades) or object motion, via
  the "phantom array" effect.[20][21] Fast-moving flickering objects
  zooming across view (either by object motion, or by eye motion such as
  rolling eyes), can cause a dotted or multicolored blur instead of a
  continuous blur, as if they were multiple objects.


You need to think not only about what the eye can directly perceive, but possible stroboscopic effects