I'm seeing more LED's in automotive use like tail lights, so that's a good sign. Seems like they've nailed down a stable driver that can handle voltage fluctuations, like on starting.
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.
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.
Does anyone else find many of these LED tail light designs too bright? I find myself squinting or outright having to look away from them, particularly when immediately behind the vehicle at an intersection.
I've seen a few designs that do not overwhelm in luminosity, but I find most of them to be an outright hazard by partially blinding those in following vehicles.
Voltage fluctuations don't matter since they're driven by a switching constant current supply. The voltage drop across one high brightness LED is only a few volts.
