Eli5 Why modern car headlights are designed as single units and not modulararly like in the past, making it so replacing the whole unit now being required if the LEDs burn out or the glass/plastic gets damaged?
It increases their lifespan under normal conditions and makes them more compact(Lighter/cheaper/smaller)
The sealed LED bulb assemblies have lifespans measured in decades rather than years like traditional halogen bulbs. Since they’re going to last the life of the car in the vast majority of situations and won’t require regular consumers to change the bulbs then making them a single sealed assembly makes them smaller and cheaper than supporting the ability to swap parts out
If the plastic is broken/damaged you likely needed to swap out the whole headlight assembly anyway even on older halogen bulb setups so there’s no gain there. Even on cars with older bulbs the lens isn’t easily swappable but the whole assembly is only a couple hundred so it isn’t worth the labor costs to pull the assembly, swap the lens, then reinstall the assembly versus just putting a new one in
Having a custom shape allows the designers to give the car the appearance of their choice. It also lets them improve the aerodynamics for better gas mileage.
Yes, they are prioritizing easy manufacturing and other aspects of how they want to the car to look/function, at the expense of being able to repair and maintain the car in the future. This is a problem for consumers.
But if it was *only* a cost cutting measure, they would probably save more money reusing an old or universal headlight instead of designing and manufacturing a new one. It’s not 100% them cheaping out or trying to prevent repair. They have other design goals that are better met with a custom shaped headlight, and they are focusing on those.
Older incandescent light bulbs have a very limited life. Typically a few hundred to perhaps a thousand hours of use. Since a car would outlast the light bulb, it made sense to design fixtures that allowed for their replacement. Bulbs were also fairly unreliable – they could fail any time.
Modern LED lights can run for tens of thousands of hours and rarely fail. As such, mechanical incidents aside, the LED light will have a good chance of outlasting a car. By designing the entire light as a replaceable module it is simpler and cheaper and probably better quality to outsource the design, manufacturing and testing to a company that has this expertise.
It is also rather expensive and time consuming to replace the LED and the associated electronics (the old type bulb simply needed 12V power and a socket to screw in) so giving a “user replaceable” LED option just makes the module more expensive. To replace a $5 bulb in a $100 old light assembly makes sense. To replace $50 LED/electronics in a $10 modern light assembly makes much less sense. Replacing the entire light assembly saves the end user repair money and time. (also most service/repair depots won’t have electronic repair capability)
Because it’s cheaper for them to manufacture one big piece than many small ones, due to production lines, cable management, body of the car, among others.