I only found mine was really poor when the lens is covered with dirt, dried up dirty water, or just after a rain and you've been driving behind another vehicle on a 40/50mph road you get the idea.
Noticed one dusk/night, the light was dull, scattered, a bit 'poo' no pun intended, on a dark highway...when the highway straighted out...i pulled the screen and headlight wash, light almost completely blacks out for a sec or so while water is being sprayed, within 5 secs or so...back to full brightness
...usually when I'm about to embark on a long highway journey at night (where there are no streetlights), where possible I would spray/throw some bottled water over them then wipe the headlights with a microfibre. If I can see the headlight mirrors clearly streak free...the lights can shine on the road well
.
I'm sure many of you have seen 10+ yr old cars with frosted/decoloured headlight plastic, even if you change to new bulb, light cannot shine as well as when new through a clear lens.
I also have an
Ibiza with Bi-Xenons, while they are marginally brighter (compared to 63 plate Leon LED lights) and shine further, Leon LEDs pick up more detail, and for me reflects the light of reflective things better. Full beam, no contest, LEDs! Bi-Xenon full beam on
Ibiza is as joke...