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AFAIK, it only takes a zener diode and a resistor to drive LEDs in an automotive application (or any automotive electronic device that runs on < 12V DC). The power is already rectified by the time it leaves the alternator. Worst case is that they're a bit dimmer than normal on startup.

Many car LED tail lights are actually refreshed at (I'm guessing) 30Hz or so to keep from overloading the wire - They have a distinct look to them from the low refresh rate.

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While it's certainly possible to do so, I doubt any engineer worth his salt would actually use a zener and resistor as a stable power supply for automotive lighting. Voltage in cars varies from pretty low (sub-8 volts or so) when the starter is cranking, to around 14-16 volts when alternator is running against a fully charged battery, to the occasional high voltage peaks of 40V+ when, e.g., the air conditioner clutch disengages.

That's a pretty large range to run a current-driven device (the LED) from a fixed resistor. Most useful applications these days will use constant-current supplies that feed the LED a fixed amount of current as the input voltage changes all over the place.

Those low-hz LED tail lights drive me nuts. The strobing effects are incredibly distracting and headache-inducing.

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