The fact that the Prius got the only good rating is because Toyota has some of the best projector lenses out there plus it was running LEDs. The two Lexus cars that were "acceptable" are, I believe, still running HID tech (with projectors) and the "marginal" Camry was probably a model with projectors but running halogens. As far as Toyota is concerned the results are spot spot on.
I've driven a 2010ish Camry with halogens and projectors and I was not impressed by the headlights. I definitely feel like my 4Runner's low beams could be better...
Toyota has most of their headlights designed and built by Koito. Koito generally makes good products, but its, as with everything, a get what you pay for situation.
And the type of livht source doesnt have much to do with the end result. You can have an excellent headlight that was designed to wring maximum efficiency from a low wattage, long life bulb. You can have a shitty headlight that uses a 25 or 35 watt HID burner. You can have a good headlight from LEDs with either a projector lens or a reflector or other optic.
We are hamstrung by the regulations. FMVSS 108 is the federal regs for vehi le lighting. It is basically a list of minimal and maximal intensities at different points within the beam, at various angles, with the headlight at its intended height.
These intensity variables give a lot of wiggle room for both good and bad design.
Theres also limitations on material selection. Headlight manufacturers used to make a lot more headlights with glass lenses. Well, the molds or stanps for these lenses are expensive. They dont want to replace them, so even new headlights might be shitty and out of spec. Manufacturers started using plastic. Well, because of the length of lifecycle testing, new materials take. Lot longer to be adopted here in the US, than say the EU. We have to lay samples out in the desert of arizona and souther florida for several years. They stick them under a uv/ir lamp and heat and cool them to simulate the passage of time more efficiently and consistently. So they can use newer/better materials and UV/IR resistant coatings in the EU.
Plastic headlights here are generally polycarbonate with a UV resistant coating baked into their external coating. Its a cheap, relatively durable material. The coating wears off and gets baked away after about 5 years. Headlights begin to degrade/fog up/get sandblasted and yellowed in appearance. This cuts down the amount of light on the road significantly.
Sure, you can sand off the exterior oxidiation, but now youve exposed bare, untreatex polycarbonate to the sun. The process begins again, at an accelerated rate (none of the restorative kits have a uv coating that is anywhere as near as effective as the original).
And while headlivht intensities are mandated, they get tested on a bench, fed by a power supply. So companies can skimp on the wiring, or run the wiring through a janky little switch on the stalk, and you lose a lot of power, and therefore output, which means less light on the road, and a more dangerous driving experience.
As far as other lighting regs go, there is no technical definition or limits for fog lights, so most cars just have a shitty little "accessory" light. No real cut off, no real beam pattern. And even worse, no ability to turn off the low beams and use only the fogs, which most idiots on the road wouldnt know to do anyway.
Hopefully this will spark some improvements, but i doubt it.
