I don't have a Discovery, but my 2005 Airstream had really poor headlights. I polished them and that improved things a fair amount but honestly they were still borderline at best. I found out that the headlights in my Coach were from a 2005 Ford Explorer so I went online and found a direct replacement modern (OEM) headlight and had them installed. Made a huge difference. I can actually see at night if I have to drive then.
2005 Airstream 396 XL Land Yacht with Cat 330 C7
2016 Grand Design Solitude 369RL-R 5th Wheel