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Xenon lamp does not have enough on-board voltage of 14 V to burn. You have to add to the circuit so called inverters, which increase its level. They used to be 300 volt, but today they can make do with combination of 85V and 400 Hz and even 42 volt! By the way, this leads to the following conclusion: a lamp is not the same as a lamp and you have to be careful when replacing it. For example, D1, D2, D3 and D4 series lamps are not interchangeable! And on the back there is also a letter R or S which you also have to take into account.
You can't do without one inverter though: neither 42V, 85V or even 300V will punch the gap between the electrodes when the lamp is switched on. Moreover, the gap here is larger than in a spark plug, and gas pressure in the bulb is higher than in the combustion chamber. Therefore, a high-voltage (25,000 V) ignition pulse is also needed. The device that generates it can either be external (e.g. D1 lamps) or integrated (D1S lamps). Note that the breakdown voltage threshold is one of the reasons why xenon was chosen: it is the lowest among the inert gases. If there was air in the bulb, you would need much higher kilovolts at such pressure and gap! Other reasons lie in the cost and in the technology of precise gas dosing. In general, an optimal ratio was found. It is not surprising that these lights are called "xenon". Although, jumping ahead, we should say that their construction is somewhat different than that of the halogen ones.