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. Since the 1990s the exterior casings of headlights have been made from polycarbonate instead glass, as it's both lighter and stronger, while light from the headlamp bulb is aimed via a series of computer designed complex reflectors, as seen in the Ford Ranger (above, left). Alternatively the light beam can be directed by a projector lens within the headlight housing, such as the ones found in the Mazda MX-5 (above, right).
Combing low cost and a working life of between 500 and 1000 hours, halogen bulbs are the most common headlamp type in use today, although that is rapidly changing. Spurring things along is the desire of car makers to improve efficiency. Halogen bulbs draw around 55 watts of power, and much of that is wasted as it’s converted into heat rather than light.
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.
In cars HID lights contain a trace amount of the inert noble gas xenon, hence their common name: xenon headlights. Xenon gas prevents automotive HID lights from flickering when they’re switched on and ensure that an adequate amount of illumination is provided before the headlights reach maximum brightness, usually within a few minutes.
Automotive HID lamps are easy to distinguish as their cool white glow is accompanied by a distinctive blue tinge around the edges. Some cars feature only HID lighting for their low beam, with high beam provided by a separate set of halogen lamps. Bi-xenon setups, however, are able to provide both high and low beam from the same set of HID lights.
HID headlights first became available in the mid-1990s, but are now optional on most mainstream models. The rare elements employed by an HID bulb have kept prices high, giving room for newer technologies to storm the fort.
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. When LEDs are used in brake and indicator lights they're said to improve the reaction time of other road users by around 30 per cent. On top of this, some bulb makers are claiming a life of up to 15,000 hours for their LED headlamps.
Touch a halogen bulb or xenon globe when it's on and you’ll likely recoil in pain from the intense heat, but with LED headlights you’ll struggle to break a sweat. Therein lies their great advantage, they convert most of the energy directed to them into light not heat. In fact most of the heat generated by LEDs is at their electrical base, not on the bulb surface.
For the last few years LED headlights were only available on sedans retailing for north of $200,000, like the Audi A8 and Lexus LS, and the hypermilers’ best friend, the Toyota Prius. Recent advances, though, have licked earlier problems regarding brightness and rearward heat dissipation, and LED headlights are now heading toward the mainstream. This year they became available on the humble Corolla sedan, albeit only the top-of-the-range $30,990 ZR.
Later this year BMW will be the first to offer laser headlights as an option in its i8 plug-in hybrid supercar. So, yes, we’ll get the joke out of the way now: this car has freakin’ lasers in its eyes.
But before Dr Evil starts whipping up some convoluted scheme to extort a few hundred thousand dollars out of the poor citizens of planet Earth, he should realise that BMW isn’t planning to shoot flesh cutting laser beams down the road.
Rather the laser beams are focused towards a cloud of yellow phosphorous gas. When excited by the laser the gas emits a powerful white glow, which is then reflected and diffused to light up the road ahead.
Initially this laser light system will only be used for the high beam. BMW claims that the new headlamps are smaller, more energy efficient and can illuminate the road up to 600 metres ahead of the i8. By comparison the i8’s regular LED high beams can only manage 300 metres.
Headlight conversion kits
If all this talk of more efficient, yet brighter, headlights has got you all excited and thinking of ways to upgrade your current steed, you should probably think again.
Although there's an aftermarket willing to cater to your desires, upgrading to a different type of headlight technology will almost certainly put you in contravention of the Australian Design Rules (ADRs). Indeed some online headlight stores warn buyers that their products are only legal for off-road use.
In relation to headlights, the ADRs dictate the size and shape of a car headlight’s beam, as well as the maximum amount of permissible glare to oncoming traffic. For headlights with an output over 2000 lumens (that’s all HID units, basically) a headlamp washer and self levelling system is required, and cars sold with halogen lights usually aren’t equipped with either feature.
If that’s not enough to dissuade you, think of your fellow road users. Headlight reflectors and lenses are designed for a bulb of a specific output, size and shape. Altering any one of those elements may result in a different beam pattern that could stun, blind and annoy other road users.