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!