Tired HID xenons

[asklepios]

My S6 HID dipped xenons are frankly rubbish. Main(non xenon) fine. Do these fatigue in service? I am imagining the worn spark plug as an analogy.

[gazza57]

Xenons should not degrade except after many 1000's of hours service.
Your analogy of a spark plug is not exactly correct. The control circuitry consists of a switch and ballast unit which in essence is a large transformer which has it's primary winding switched very rapidly,the resulting collapsing magnetic field generates an extremely high voltage probably more than 2500v at switch on only.
When 12 volts DC is applied to the input terminals of the ballast unit it is switched very quickly which causes a high voltage spike to be generated from the ballast unit and applied across the electrodes in the lamp which are filled with Xenon Gas, the gas is ionised and a current flows between the electrodes and this causes the ionised gas inside the lamp to glow brightly. The ballast unit is switched out of the circuit immediately and the Xenon Gas lamp will glow under it's own power until the 12VDC is removed. ie when you switch off the lights.
You could have some lamps which are suffering from low xenon pressure and therefore won't glow as brightly.
Are both lamps dim or just one?
Have you tried swapping a lamp for a new one to see whether the new lamp glows more brightly than the old one?
If the output from the ballast was low the lamps would have difficulty in striking, rather like a faulty flourescent lamp in fact the design of the Xenons are identical with the exception of the gas which fills the discharge tube.
try these tests first
Gazza57

[asklepios]

Gazza ,thanks for comprehensive reply. Understand my analogy flawed as arc only at start up. Follow fluorescent light idea, and certainly observe that they dim in service.
Both dim , but originals (127k miles). Will splash out on one and see !

Thx for helphttp://www.vwaudiforum.co.uk/forum/images/icons/icon14.gif

Asklepios

[asklepios]

New bulbs,at great expense produced a massive improvement.
Old units appeared milky and deformed , much like the flash cube of old. If yours look like this I would urge you to bite the bullet and buy new bulbs.