Narrative:

Flying behind a 3 blade prop I observed the following visual effect of the led runway lights:on the previous evening I was transiting the final approach path of kpae rw 16R and observed the runway edge and center line lights cycle on and off in entirety at a rate of approx 1 [per] second. This was observed as very similar to the rate of a blinking traffic light at a 4-way vehicle stop. Prop speed was 2400 RPM. This was observed through the entirety of the front windscreen and at least part of the pilot side window. I queried ATC about the reason for the runway lights blinking and was told that they were not blinking. It was not immediately obvious what was causing this; but I did later speculate it may have been caused by looking through the prop arc.during this flight (next day IFR training) while on the VOR16R approach we observed the runway edge and center line lights cycle on and off in entirety at a rate slightly faster than 1 [per] second. Prop speed was 2500 RPM. I then varied the prop speed and found that at 2700 RPM the lights were observed strobing at a fairly high rate; and at 2000 RPM the blinking rate slowed to less than once per second. This was observed through the entire approach that terminated at the map. The flight instructor was also surprised and mentioned that he had not seen this before; but he also doesn't spend much time behind a 3 blade prop arc.I would speculate that the pulse width modulation (pwm) dimming system of the led runway lights was phasing with my propeller causing the observed effect. I would also speculate the effect would be significantly different at other led dimming settings as this would change the frequency of the pwm modulation. I would also expect a significantly different effect behind a 2 blade prop.I found the effect to be entirely confusing and distracting and would not want to make a landing in such conditions.

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Original NASA ASRS Text

Title: A Bonanza pilot reported that he observed the runway edge and centerline lights 'strobing;' possibly due to viewing a pulse width modulated set of lights through a 3-bladed propeller.

Narrative: Flying behind a 3 blade prop I observed the following visual effect of the LED runway lights:On the previous evening I was transiting the final approach path of KPAE RW 16R and observed the runway edge and center line lights cycle on and off in entirety at a rate of approx 1 [per] second. This was observed as very similar to the rate of a blinking traffic light at a 4-way vehicle stop. Prop speed was 2400 RPM. This was observed through the entirety of the front windscreen and at least part of the pilot side window. I queried ATC about the reason for the runway lights blinking and was told that they were not blinking. It was not immediately obvious what was causing this; but I did later speculate it may have been caused by looking through the prop arc.During this flight (next day IFR training) while on the VOR16R approach we observed the runway edge and center line lights cycle on and off in entirety at a rate slightly faster than 1 [per] second. Prop speed was 2500 RPM. I then varied the prop speed and found that at 2700 RPM the lights were observed strobing at a fairly high rate; and at 2000 RPM the blinking rate slowed to less than once per second. This was observed through the entire approach that terminated at the MAP. The flight instructor was also surprised and mentioned that he had not seen this before; but he also doesn't spend much time behind a 3 blade prop arc.I would speculate that the Pulse Width Modulation (PWM) dimming system of the LED runway lights was phasing with my propeller causing the observed effect. I would also speculate the effect would be significantly different at other LED dimming settings as this would change the frequency of the PWM modulation. I would also expect a significantly different effect behind a 2 blade prop.I found the effect to be entirely confusing and distracting and would not want to make a landing in such conditions.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.