Why cheap plastic headlights?

Hi,
I’m an owner of 1993 year vehicle. It seems to me that most automakers are outfitting their car with >ahem< crappy plastic material. Crappy because as it ages the plastic yellows and obscures transparency of the lens.

For awhile I thought it was only me, but it seems this happens with any headlight I’ve seen so far.

I understand about costs, but this becomes a serious safety issue if you actually take care of your car long enough for such a thing to happen.

Manufacturers of course recommend replacing them when this happens (at a premium), I’ve seen do it yourself lens cleaning tutorials- but it’s not the point I’m making here.

Someone must have caught-on by now that their plastic yellows with exposure to heat and sun.
Why do the car makers still insist on using this plastic formula?

Because it is as you noted, cheap. That and they don’t start turning yellow until your car warrenty has expired.

It is cheaper for them because the plastic unit can be added to other modules, like the radiator assembly and delivered to the factory as part of a larger unit that is easily installed instead of have to mount the old style glass bulbs one at a time on final asembly line. The price of progress.

(Deleted pointless, cynical message)

Used to be, vehicle designers fit standard round or rectangular lamps into the front end. Those headlights had glass lenses and could be made cheaply because the lenses weren’t very big and there were only four basic types (large round, small round, large rectangular, small rectangular). Of course, this was rather limiting on the artistic side of sculpting a front end shape.

With modern car design, headlights are part of the body outline. The size and shape of the lenses differ from model to model, and tend to have a lot surface area compared to the old standardized units. Making them of glass would be a lot costlier. But plastic is also more forgiving of love taps, and the likelihood is that on average, plastic lenses go far longer before getting cloudy and yellowed than glass ones would go before getting broken.

I think it improves the aerodynamics (and therefore fuel economy) of the car as well, not just the aesthetics.

Plastic is also lighter than glass and thus contributes (slightly) to the fuel economy of the car. More importantly, however, it enables the car companies to ship more of the headlights using less fuel, so their shipping costs are lower.

I wondered if it might somehow be related to the chipped windshield phenomenon as discussed in a recent thread.

Well, if it has to be plastic, is there not a formula out there that could “act like” glass?

Another compound to be added in the usual formula or what not?

I’ll be the first to agree with Gary T; it is more resililent, but headlights as mentioned also take up more real estate on a vehicle’s surface area now making them not cheap.

Either carmakers need new technologies that don’t create so much heat- thus making the material that much more clear, for longer or they need a better plastic mixture that behaves enough like glass that it will not change color.

There are coatings that could be applied- my point?
Cars are being built every year it seems with cheaper, lighter and LESS materials and yet the price of that new vehicle seems to remain practically the same.

They could accomplish such a thing (I believe) rather cheaply if there cared enough to put some thought into it.

Right now though it only cost us money and I’m quite sure car makers everywhere are just fine with that because who’s going to say anything about it?

It could be an accident, it is unlikely that anyone did a 14 year test on various plastics before selecting the specification.

For example a UK manufacturer of kettles came up with a plastic electic kettle called ‘The Swan’, they were very proud of it, test marketed in Scotland where it sold like hot cakes.

After about six months they started getting complaints, it seemed that kettles tended to be placed in windows and the plastic decayed in sunlight.

They had tested it for heat, corrosives etc, but nobody had thought of sticking it in ultraviolet light for six months.

It’s a 1993 car. Plastics have come a long way since then. However I don’t suppose I can really provide evidence until 2021…

Even a glass windshield will get sandblasted over time, which will distort the optical quality.

I have had such headlights ‘renewed’ by using a polisher, the yellow was gone, along with most of the pitted surface.

Advance Auto article on lens cleaning here

I’m sure they do accelerated tests, using high heat, repeated temperature cycles, intense UV, etc. to simulate effects of aging. It’s not perfect, but it’s usually helpful.

My point is that they don’t think of doing the one test that screws things up in the wild. It is a variation of Sod’s Law.