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Donald
02-23-2015, 09:10 PM
I have noticed that LED running lights on new cars, when shown in slo-mo, pulsate. Are they not DC powered? I expect anything powered by AC to pulsate, but not DC.

I just took a slo-mo video of a LED flashlight with my iPad and it did not pulsate.
fastblackmerc
02-24-2015, 04:02 AM
I have noticed that LED running lights on new cars, when shown in slo-mo, pulsate. Are they not DC powered? I expect anything powered by AC to pulsate, but not DC.

I just took a slo-mo video of a LED flashlight with my iPad and it did not pulsate.

I have many LEDs in my Marauder and none pulsate. I have seen cheap LEDs that will pulsate over time. Could also be a bad connection.
rauder88
02-24-2015, 08:07 AM
Most LED running lights are PWM they appear "dim" to us because we cant see it flash it just appears dim. Your flashlight doesn't flash because it is running full power. Interior lights will not flash because they are controlled by a resistor that restricts the voltage.
Donald
02-24-2015, 01:11 PM
rauder88,

The resistor drops the voltage across the LED and the current running thru it. Does not change the wave form that is the cause of pulsing. Your mention of PWM explains all.

http://en.wikipedia.org/wiki/Pulse-width_modulation

Our eyes have persistence which means we don't see fluctuations in brightness above a given frequency. The slo-mo filming does.

Thanks.
rauder88
02-24-2015, 01:54 PM
rauder88,

The resistor drops the voltage across the LED and the current running thru it. Does not change the wave form that is the cause of pulsing. Your mention of PWM explains all.

http://en.wikipedia.org/wiki/Pulse-width_modulation

Our eyes have persistence which means we don't see fluctuations in brightness above a given frequency. The slo-mo filming does.

Thanks.

Yep. On a few exhaust videos I have done of my mustang in real time you can also catch the flicker, really shows up in slow motion though.