Beaming at performance and safety

Geneva Motor Show displays widespread adoption of xenon and LED lighting

By Philippa Martin-King

On the lookout for bling-bling, the flashy, extremes in performance, superlatives in whatever sense, some of the visitors to the 2012 International Motor Show in Geneva might have been disappointed to find few novelties and little innovation. It wasn't immediately apparent that they were witnessing the start of a new era or the culmination of many years of research and development destined to make the driving experience more economical, safer and easier. Some of the features that might once have been labelled "sensationalist" or "experimental" have reached the public at large.

Several examples of car lighting Several examples of car lighting

More with less

Nearly every exhibitor had at least one economical or "green" automobile model or some sort of safety improvement on show. Most were claiming to deliver "more with less" and promoting increased energy efficiency with greater fuel economy. At the same time, there was a strong accent on using automated systems to provide ever improving levels of safety. Constructors had erected information panels showing the ratings and comparing the energy measurements of each vehicle on display. To improve energy use implies not only controlling the performance of the engine and making tuning refinements to cut down on fuel use, but – on a smaller scale – improving the performance of the growing number of additional electrical systems that are installed in a vehicle.

Improved lighting reduces cost

One of the areas in which energy efficient technological innovation has clearly made its way into the commercial market is in lighting. Less than a decade ago, only the top of the range vehicle was equipped with xenon lights and LED lighting was still at an experimental stage. The first xenon headlights appeared in the European market in 1991 as an option. The normal household car still came equipped with standard traditional halogen filament light bulbs. In a period of just a few years, that norm has changed. There are two main advantages: one of energy efficiency, the other of security. Both are of benefit to all road users, not just to the individual vehicle owner and driver. Better lighting implies both seeing and being seen: a better view of the road ahead and also increased visibility for the oncoming driver. Better energy efficiency implies reduced running costs. 

Xenon is an example of HID (high intensity discharge) lighting. The lamps work on the basis of an electric current that, in the form of a spark, ionizes a gas environment (xenon) and sets off an electric arc. It is the arc that provides the light that can then be reflected and beamed, while traditional halogen bulbs use the principle of heat to generate light from the tungsten filament.

The higher luminous efficacy of xenon

Xenon has the advantage of having a much higher lighting capacity than halogen. 30% of the absorbed electric energy is transformed into light against only 10% for a halogen bulb. The result is that a xenon bulb will produce a luminous flux of 3 000 lumens with an electric power of 35 watts as compared to a tungsten halogen bulb that only generates 1 450 lumens with a power of 55 watts.

Longer bulb life

There is a second advantage to xenon lighting: that of bulb lifetime. The average lifetime of a xenon bulb is 2 500 hours against 500 for a halogen bulb. For halogen, many manufacturers also recommend that their bulbs be replaced every three years as a precautionary measure. Replacing bulbs with new ones ensures that the cut-off line set for the aligned beam of dipped headlights remains at the level required for optimum visibility and that there is no tilting that would affect visibility performance adversely. With xenon lighting there is no risk of tilting with time.

Improved colour temperature

Because the CCT (correlated colour temperature) of xenon lighting is higher than that of a halogen bulb, it is said to be easier to perceive and differentiate the colours that are illuminated. Some constructors even talk of "daylight colours" although this is not technically correct because the CRI (colour rendering index) is not as close to daylight as with halogen. What is certain is that being able to see objects more clearly offers an advantage when driving at night in dark conditions. Drivers are able to react faster and more accurately to external sources of danger.

Dealing with the dangers of visual colour perception in the half-light

In their paper, the first prize winners of the 2006 IEC Centenary Challenge, George Zissis and Stuart Mucklejohn, wrote about the dim half-light that occurs between day and night and in which the human eye is totally incapable of perceiving certain colours correctly. Under the title,Standardizing mesopic vision conditions and incidences on light sources science and technology,they argued that new standards need to be produced and are important as a safety measure, covering that particular type of light. They postulated that the lack of relevant publications is slowing down the development of new product development and with it energy economies and means of sustainable development.

IEC TC 34: Lamps and related equipment, is responsible for a 2012 Technical Report,IEC/TR 62732, that describes how to construct a three-digit code in the form of a shorthand string that combines the nominal general CRI and the nominal CCT.

Dangers of being dazzled

There are also some negative aspects associated with xenon lighting. Drivers of oncoming vehicles can be momentarily dazzled by the high intensity light it generates and the flashing effect that is created when a driver changes between raised and dipped headlights. 

There's also a split second wait between the moment the light is turned on and when it obtains full illumination, which explains why certain constructors have chosen to install in cars dual filament xenon reflector headlamps known as BiXenon or BiHalogen projectors. These combine a single reflector with various methods for controlling the angle of light beam, depending on whether the light is dipped or full.

Higher voltage needed

Generating the electric arc of the xenon lighting requires a high voltage. The 12 volts of the classic car battery isn't sufficient, so the voltage needs to be converted and raised to 85 V. This requires the installation of an additional controller and transformer. 

Further accessories may also be required with xenon lighting. Although more economical, safer and more reliable than traditional halogen, legislation designed to reduce glare sometimes makes it compulsory for the headlights to be equipped with a lens washer and an automatic beam height regulator. In cold weather, when there are snowy conditions, the heat generated by the halogen headlight simply melts away the icy covering while the xenon light continues shining brightly… but coldly.

Conformity assessment and recognized labelling important

Because safety is such an important aspect of lighting for road users, constructors and authorities underline the importance of ensuring that any headlight installed in kit form carries the necessary approvals and recognized labelling, based on official conformity assessment. Some countries ensure that this is respected by carrying out official controls backed by vehicle certification when the vehicle is presented for its periodic check-up.

LEDs reduce energy consumption

Another lighting solution was demonstrated widely at the 2012 Geneva Motor Show. LED (light emitting diode) lights were evident not only as rear lights, but as headlights too. Installing LEDs as an alternative solution to the traditional filament bulb is another means of improving energy efficiency and lowering fuel consumption. LEDs use the light emission properties of particular semiconductor materials. They have a high luminous efficacy which is not affected by erosion, vibration or use.

In comparison to the halogen bulb’s lifespan of 500 hours and the xenon bulb’s 2 500 hours, an LED is estimated to have a lifespan of some 10 000 hours. 

LEDs have a low power draw which makes them particularly economical. For an equivalent output of light intensity, LEDs use 80 % less energy than a halogen bulb and 60 % less than xenon lighting. In addition, LEDs light up 200 milliseconds (0,2 second) faster than incandescent bulbs, which, while it may not be fully perceived by the human eye, still provides an advantage when the lights are used as stop lights, by providing a split second of extra time in which to react. It also opens up new possibilities for providing intelligent automatic control when dipping and raising headlight beams.

A colour for every condition

Finally, LEDs offer a multitude of possible colour temperatures. The resultant light gives better colour perception of objects and thus a higher margin of safety. LED lights can be combined into different strips and so into different colour combinations that may be more suitable for coping with difficult light conditions such as fog or snow.

LED lighting is changing the general approach to safety. The likelihood is that at one of the next International Motor Shows, visitors will find themselves confronted with a new safety arrangement of standard LED lighting – for example working in conjunction with an infrared camera. Perhaps one day they'll be able to sit back and put their car on automatic pilot to drive them securely to their destination – while they shut their eyes and take a rest.

Several examples of car lighting Several examples of car lighting