- Jan 1, 1970
Turboprops maintain a steady RPM and vary their prop blade pitch to
adjust thrust, so I could see a turboprop having a distinct frequency.
Less so for regular piston aircraft.
Prior to LED lighting being used outdoors, I think it would be safe to
assume any flickering light faster than a few hundred Hz would be prop
reflection. Nowadays it may be more complicated. Even street lights
these days are LED based.
Most LEDs are flashed, though the arguments seem endless if DC or
flashed LEDs are better. Supposedly the eye detects the peak intensity,
so you can PWM the LED for better effective illumination. But I have
seen arguments that DC is better.
I tested a number of LEDs to answer that. Basically, pulsing mostly
just increases i^2*r losses, with few exceptions.