The question is in the subject.

@James? @RRK?

Anyone?

Discharge lamps that contain XE not as a buffer gas but for creating light (spectrum completion) need to have at least 60 bar/870 psi when at operating temperature.

@StefanE: In automotive MH lamps, the xenon is there to provide minimal amount of light at turning on, so it is a buffer gas, and isn't produces light once the mercury and the halides evaporated.

Yes that's correct. However, Xenon under atmospheric pressure does have most of it's spectrum in the infrared region, above 950 nm.

When under low pressure, such as LPS, HPS, some rare FL or even in industrial cold cathode lamps, Xenon is only used as a buffer gas,
that means like 95% the gas decelerates the ion movement and 5% is creation of light by electric discharge. Not very efficient.

When you raise the pressure, the ability for gas discharge becomes way more prominent, also the spectrum gets shoved into a more useful
range of wavelengths. You will need to have at least 20 bar or more for this effect to come into existence, more like 60 bar to really
create light efficiently from Xenon.

Xenon short arc lamps have a cold pressure of around 8 bar and a hot pressure of 60-80 bar, they are very efficient with no other gasses
present. Some ultra high pressure Xenon lamps (mostly text equipment in labs) run up to 200 bar and create a near sun-like light ... but
they are ungodly expensive.

Have you tried applying high voltage to a Xenon flash tube? You will see a faint glow, for the human eye it looks blue-ish since we
cannot see the 'red' of 950 nm and above. When you pass a very high current through the ionized Xenon gas, the pressure will spike by
around 40 bar in the plasma channel (of larger standard flash tubes like photo equipment or disco flashers). This is when Xenon becomes
efficient in creating visible light.

So the 'cold' pressure of an automotive MH lamp is already very high - the Xenon provides a substantial part of the overall light output.
Also, Xenon car lights are heavily boosted by their electronic ballasts.