Xenon lamp
A xenon lamp is a gas-discharge lamp, which is particularly well known as a light source in headlights. Unlike a halogen lamp, the light is not produced by a glowing tungsten filament, but by an electrical discharge between two electrodes.
In the xenon lamps used in vehicle headlights, the burner contains, amongst other things, the noble gas xenon. This enables light to be emitted immediately after ignition. During operation, other components of the gas mixture contribute significantly to the lamp’s photometric properties.
Ignition and warm-up phase
A high ignition voltage is required to start a xenon lamp. This ionises the gas filling between the electrodes and triggers an electrical discharge.
Immediately after ignition, the lamp has not yet reached its normal operating state. As the temperature rises, further components of the gas mixture vaporise, and both the light output and the colour of the light change until the intended operating state is established.
For ignition and operation, a xenon light therefore requires an electronic ballast, which provides the necessary electrical conditions and regulates the light’s operation.
Xenon light in headlights
Compared with halogen lamps, xenon lamps offer higher luminous efficacy and a high luminous flux with comparatively low electrical power consumption. Furthermore, they generally have a longer service life than halogen lamps.
The perceived colour of the light also differs from that of many halogen bulbs. However, the exact colour temperature depends on the specific bulb type and operating conditions and cannot be deduced solely from the term ‘xenon’.
Xenon bulbs are used in particular for low beam and high beam in headlights. Systems in which a single xenon light source performs both lighting functions are often referred to as bi-xenon headlights. In this case, there is no switching between two filaments; instead, the light distribution is altered, for example, by a mechanically moved shutter.
Designs and labelling
Xenon lamps for vehicle headlamps are available in various standardised designs.
Well-known designations include, for example, D1S, D2S, D3S or D4S, as well as corresponding variants with different base or optical designs.
In older, type-approved xenon lights, designations such as DC, DR or DCR may indicate low beam, high beam or a combination of both functions using a gas-discharge light source. Further information on this can be found under indications on lights.
Today, xenon bulbs are largely being replaced by LEDs in new headlamp designs. However, they are still in use in numerous existing vehicles.