>LEDs are... a rounding error against a car’s total energy usage

It's more about economizing the power supply package and heatsink integrated within the bulb or lamp assembly.

Yes, this is the real answer. Most LEDs do not operate well at high temperature, unlike incandescent bulbs or HID bulbs (which can both operate inside ovens, if you need them to). A headlight designed for incandescent or HID will not provide enough cooling for LED lamps unless the LED lamps are efficient enough.

> which can be recharged off of otherwise-wasted energy from the engine idling

That’s not how it works. When charging, the alternator will put more load on the engine and that will increase fuel input to keep rpm up enough to keep the engine from stalling.

Overall, every vehicle designer will seek to minimize any and all loads (even small ones).

Worst is when they remove the spare tire, grrrrrr.

The brave new world is cans of fix a flat as far as the eye can see.

Some people seem to take pride in not noticing subtle visual and auditory effects.

I envy those people. This world is getting noisier every day.

> Wait, what? They are economizing on headlight LED power draw?

Mass produced cars have reached the point that a $0.50 saving per vehicle is worth designing and building for. When you reduce the current draw from something that is always-on (like headlights) you increase the life of the LED, you can reduce the gauge (size) of the wires to the lights, you can reduce the size of the alternator, you can load the alternator less, which means increase the service life of the alternator belt and idlers, and (in theory, at least) decrease fuel consumption.

All of these are tiny, tiny efficiencies, but they do add up.

While it might seem penny-wise and pound-foolish, imagine following this same logic for all systems in a modern vehicle. This is why even such a "rugged offroad" vehicle as a Jeep Wrangler has a plastic clutch slave cylinder (weight and cost savings) and why the headlights will dim in virtually all vehicles if you turn on every single electrical device that draws current (the wires are not sufficient gauge for everything to draw max current at the same time).

They're saving actual money on every vehicle built, which is what they care about.

A lot of modern cars only have a single LED bulb that provides normal headlights and high beams. In the past with halogen headlights they'd either have two separate bulbs or a single complex bulb with two different filaments for normal and high beams. I would assume LED + PWM lets them have a single bulb whose brightness can be controlled by software, so the choice is probably more about cost savings and reducing complexity than energy usage.

I don't have a car with LED bulb so I can't check, but I wonder how would one bulb works when normal and high beams have different beam pattern. One might be able to accomplish that with one LED bulb if it switches on/off certain LEDs in the module or the bulb is movable, but then no PWM is required.

A typical pre-LED solution is a projector and a mechanical plate that moves (very quickly) to block or unblock the part of the light that makes up the high beam coverage.

LEDs can be done similarly, but an LED matrix headlight just controls which rows of LEDs are lit up (e.g. the Samsung PixCell light that Tesla uses on the Model 3/Y). This is where we'll maybe see adaptive headlights, too, though in the case of Tesla I don't believe they've ever been used anywhere in the world, legal or not. Just to write "TESLA" on the wall when you do the Light Show.

It does seem entirely overkill to not just install a second LED. That's how bulbs have worked for years. So instead of just adding _one_ additional LED we're going to oversize that LED and then use a high frequency driver to turn it on and off really fast?