This is interesting. According to the 2001 MB S-class brochure, this vehicle comes with xenon fromt reading lights to " provide a quality of light that more closely resembles natural daylight. I immediately made the jump to WOW miniature xenon discharge klamps just like the headlights. Wow what an expensive solution to a reading lamp. Wrong!. They came on and looked very mucht like regular incandescent bulbs. Well...being an old time chemist with access to all kinds of bizarre equipment I used a portable spectrograph and inspected the light with that. ( I probable could have just as well checked the bulb for a filament but this was more fun)! Indeed the light showed the typical continuous spectrum just like any other incandescent lamp. I guess the xenon is the filling in the envelope.
As I had the instrument, I checked the headlights and saw the typical lines of a gas discharge lamps with lines in the indigo, blue green etc to make the strong blue-white
That's the story!