Technical > Automotive > Headlight output degradadation over time?

Have you replaced the bulbs? Or are they originals? All headlights, and any light in general, will dim over time. They can also yellow, develop a dark film on the interior of the bulb, and collect dirt on the exterior.

If it's been a year or two, just replace the bulbs. I prefer the "cooler" color temperature bulbs that produce the whiter light such as Sylvania's SilverStar bulbs, but that's just my preference.