According to USA Today, today, (citing a AAA study) an 11 year-old car’s headlights are throwing only 22% of the light that they did when new! The reason is deteriorating headlamp capsules.
That’s a 78% reduction in light output, if my mental math is still okay at my advanced age! Yikes!
The article compares improving the lights by replacement (OEM or aftermarket) and by restoration methods. Interesting!
CSA
It’s amazing how many cars I see running around with opaque headlights. I mean… Don’t people know that you can fix that in less than half an hour per light?
That would require actual WORK, don’t ya know! 
The worst headlight lenses I’ve seen in the sunshine state are on cars that appear never to get washed, let alone a little elbow grease applied to the headlights!
Wet roads and oncoming headlights my biggest problem. Oncoming headlights seem to blur and overpower my headlights. Only see out of one eye adequately, and the eye doctor says 5% chance of blindness in my seeing eye is too much. I can navigate ok at night but avoid it as much as possible, as I know I am impaired.
My 31-year-old headlights are as bright as new.
I think car companies should ditch composite lenses and come up with some creative glass ones
Won’t happen. Glass is more expensive, especially if you shape it anything other than “round” or “square.”
But, my 11 year old plastic headlights still look new, because I take care of them. Wax your headlights, people. That’ll prevent the yellowing.
Glass is heavier than plastic and fuel economy numbers dictate that the lightest possible materials must be used. Glass lenses are also a safety issue as they generate dangerous pieces of broken glass in frontal collisions, especially with pedestrians. Ouch!
We will probably never see glass lenses for headlights ever again. I have found that letting a body shop sand and clearcoat lenses (at $50 each) provides many years of clear lenses.
I agree it will never happen, and what you can do to prevent it. I have also noticed not all composite headlights do this? I have a 1998 chevy Prizm which headlights look crystal clear. It has spent a good portion of its life in the sun. Then I also have a 2002 Lexus that has to have it’s headlights resurfaced annually? There must be a composite material that all makers could use that does not age this way. I am sure if it was mandated they would find the solution. Majority of drivers on the road will not do what is needed to keep their lenses in top shape.
Headlights come from the factory with a coating on them that prevents UV damage. Once you resurface the headlight, you remove that coating and then are stuck doing it over and over again.
I’m really, really meticulous about how I treat my plastic headlights. I wash and wax them like the rest of the car. I never use a stiff-bristle snow brush to get snow off of them (usually not an issue as it’s kept in a garage, but if a snowstorm hits while I’m out, I spray 'em with low-temp washer fluid and dissolve the snow off that way, then re-wax as soon as I get home). So 11 years on and the original UV coating is still there doing its job. But most people aren’t that insane, and so their headlights tend to deteriorate faster.
Actually, the wax will function as a UV protectant for the plastic lenses underneath. The UV light can’t get through the wax layer without reacting with the molecules it collides with. Since the wax is replaced whenever the headlights are done, the UV protecting layer is new abut 4 times a year.
Yes, but that’s assuming the headlights get waxed. Most people don’t even wax the paint. 
I was commenting on your practice and not on what anyone else does.