David
Welcome, I am a young 72 years.
As regards your headlights; Are you sure they are LED`s, as I would expect LED`s to be brighter than Halogen.
I very recently posted an article in "Non Jaguar" section regarding headlights and the swopping of bulb types and still being legal.
My S Type had what I thought was poor headlights and I was considering changing to LED`s , which incidentally would have not been road legal. It would however seem that not everyone is concerned about that. Anyway, more to the point and may be helping you with your lack of headlight power. With my S Type I eventually found that my poor lighting was mainly due to the fact that the headlights were not adjusted properly for beam level. Having put that right it made my headlights very good. I also fitted RING Xenon 200 bulbs (readily available from Ebay and not expensive for Halogen) to the dipped beam for improved performance. They are Halogen and therefore legal for the S Type. I do not actually know for sure what genre of headlamp bulbs are fitted to your XF, but they should be readily identifiable. If you read the article I posted you will find a well known bulb supplier "link" on there and they are very very helpful with providing assistance in choice of bulbs and giving you information on what your car will need in the way of bulbs. I actually purchased my bulbs direct from them on line.
Hope this may assist a little. Best Wishes and Regards, John