I logged on with the intention of asking this question and there is an old resurrected thread on headlight mods on the front page....BUT....it is all about how to make them look better which I am not even remotely interested in. I want to get better light output out of my high beams. I've been quite disappointed in the light output for a high-end car from 2008; my wife had a government fleet car in about 2008, a basic Ford Falcon wagon, and the headlights on that would have put the ones on my XF SV8 to shame. I don't know whether mine are halogen, HID or what- how do I tell? And what have others done to get a better light output from this model? The reflectors are very small which is probably not a good starting point, but I did expect better and open road driving at night is a frustration compared to the lights on my LR Defender. Not sure a pair of Super Oscars in front of the grille would be the go on the Jag though.

 

For high beams, LEDs are the way forward. I bought for mine and I'm utterly staggered at the light from them.

 

I'm fairly sure the SV8 came with the same headlights as the later XFR (I had an XFR), which is bi-xenon (HID) low beams and ordinary H7 halogen high beams.
Bi-xenon means that the HID globe has two settings, one for low beam and one for high beam, so with high beam on all four headlight globes are on.
To check open the bonnet (hood for you Yanks!) and remove the round plastic dust cover from the rear of one of the headlight clusters - about a quarter turn (I forget which direction!) and it pops off. Then look inside with a torch at the backs of the globes, if you have HIDs you will see a largish square silver box which is the igniter behind the outer light globe. Also, look on top of the light cluster where there should be a sticker, and if you have HIDs it should say something like "Osram Xenarc D1S".
One thing you can try is to check the angle of the light pattern, it's very common for XFs to leave the factory with the headlights pointing way down and that might just explain your poor high beams. Very easy to adjust up, you need a longish 6 mm hex or Allen key which you stick in the adjuster socket and turn. I can't remember which socket (one each side for up/down and one each side for left/right) and which way to turn, but someone here will know!
Also, if the halogens are still the originals they are way overdue for replacement so consider that first before going for the expensive LED upgrade.
From memory it's possible to replace the H7 globes without removing the clusters from the car but you need skinny hands and fingers as there is very little room to move.
Much easier once you remove the clusters from the car which is not a difficult job, I did it dozens of times on the XFS and XFR.
After all that davetibbs' suggestion of LEDs is a good idea if you do lots of country/high beam driving, and you will definitely need to remove the clusters to fit them.

 

If it is the bi xenon then the full beams are excellent. So something is prob wrong. Best place to start / run car, stand in front and have someone toggle between dipped and full. On full all four headlights should light, on dipped two go off and the other two dip down. Should be pretty easy to see what's not working

 

Don't forget to aim them properly too!

On my 2014 XJR I updated to the later factory LED headlights. Very big improvement but I still could not see that well and thought it was my eyes.
But after fiddling around trying to figure out how to aim them. Turns out they were WAY low!
Moved them up several inches and I still don't get flashed much on high beams so I think I could go up a bit more.
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Thanks for the replies. I appear to have the HID outer lamps (high/low) and halogen inner lamps (high beam). I will check the aim of the lamps, but I'm thinking I will replace the inner bulbs with LEDs. Low beam is not a problem but I'm hoping for more output on high beam. The LEDs in the link above are unavailable; can anyone advise whether these appear to be suitable for the high beams https://www.ebay.com.au/itm/NOVSIGHT...U7GS#vi-ilComp

 

Aim of the lamps usually helps with low beam 'throw' as they are sometimes dipped down too far. I don't think you'll see much difference on high beam - they would have to be very out of alignment!
Still thinking something is wrong - 2x halogens plus 2x full beam HID is a lot of light power. It should be very bright!

Maybe your halogens have aged and are dim / blackened. They are cheap and easy to change.
Just to confirm, when you put the full beams on you get all 4 lights on full?

One other thought - one of the bolts that holds the light unit under the hood goes through a plastic tab that breaks easily with age. Is it possible your whole headlight unit is crooked? I had one broken tab and missing the screw that goes through the wheel arch. I didn't realize for a while that it wasn't quite in the right place...

 

I'll check but I'm pretty sure there is nothing broken with regard to the mounts. All four lights come on with high beam, also there is a difference in the outer lamps between low and high beam so all appears to be working as it should. The bulbs in the inner lamps are definitely halogens, there is a label on the headlamp assembly that states (amongst many symbols and letters) 'HID' so presumably that is what is in the outer lamps. The lens in the outer lamps is quite opaque, like bathroom glass, but from online images that appears to be normal, yes?
I have ordered a pair of LED bulbs for the high beams. I have some leave coming up in a couple of weeks so will have a chance to fiddle with this, as well as the central locking (also ordered a lock actuator for the LHR door) and the driver's window regulator.

 

Dave, can I confirm that the bulbs in your link are the correct ones for the inner, high beam, location? They showed nil stock initially when you posted that so I ordered a pair of the same make from another seller and they are incorrect fitment- if these are the correct ones, I'll see if they can exchange for that model.
Oh, and I checked the aim of the lamps- they are dead level on high beam so correctly aimed. The existing high beam bulbs are 55w halogen.