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It wasn’t that long ago that headlights were a no-thought-required feature. All cars had them and no one really paid them much heed unless they failed or were shaped in a particularly ugly manner.
Halogen
Reliably generating light with the limited resources at a car’s disposal was a problem for early automotive engineers.
Tungsten filaments, similar to the kind found in household incandescent light bulbs, were finally settled on as the solution. From the mid-1960s until now these tungsten filaments have been encased in a bubble of halogen gas in order to improve performance and longevity.
For much of their history, tungsten and halogen lamps focused light on the road via a lens that doubled as the headlight’s protective housing; now the two jobs are separate.
High intensity discharge
In high intensity discharge (HID) headlights, such as those used across the Lexus IS range, a mixture of rare metals and gases are heated to produce a bright white glow. HIDs are around two to three times brighter than halogen lamps and their glare can be particularly annoying for other road users. As such, the Australian Design Rules require cars equipped with HIDs to also have a self-levelling mechanism and a headlight washer. The former ensures that the headlights are always aimed towards the ground. The latter minimises the build up of dirt and grime, both of which can divert more light into the eyes of on-coming drivers.
Despite their brighter output, HID lamps require less power to operate. They generally draw about 35 watts and are said to be good for around 2000 hours of use.
LED
Light emitting diodes (LEDs) have come a long way from the simple flashing lights on beige computer cases to being key components in modern cars, phones and televisions.
Whether you realise it or not, they provide most of the lighting used in today’s instrument panels, entertainment head units and car interiors. As well, arrays of these diodes are employed in fog lamps, indicators and brake lights. Car designers love LEDs because their small size allows them to be fashioned into ever thinner and more distinctive shapes.
Although LED headlights currently fall a little short of the brightness achieved by HIDs, they hit maximum brightness within a millionth of a second compared with the half second required by incandescent and halogen lights.
Laser
In the Audi R8 LMX, laser beam is used only as a supplement to the existing LED headlights, activating only when automatic high-beam is being used with the aim to double the range of light compared with LED high-beam - to a full 500 metres.
So, how does it work?
Where many light-emitting diodes (LED) are used within a regular headlight assembly, lasers work in a different fashion. In the R8 LMX there are only four laser diodes each with a diameter of 300 micrometres, or just 0.3 millimeters - talk about tiny! They are wrapped tightly in what Audi calls a “radiation-tight aluminium module.”
Rather than pointing out towards the road like a normal beam, however, they instead are directed in a V-shape to a single point on a mirror, each strand of laser producing a wavelength of 450 nanometers.
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