LEDs light the road ahead in automotive applications (MAGAZINE)
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This article was published in the July/August 2013 issue of LEDs Magazine.
View the Table of Contents and download the PDF file of the complete July/August 2013 issue, or view the E-zine version in your browser.
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The majority of drivers feel stressed in poor visibility conditions, particularly at night when the ability to perceive and judge distance is severely impaired. Despite much lighter traffic on the roads at night, around 40% or more of all traffic fatalities occur in many countries, such as the US, during night-time hours. The strain eases and safety greatly increases if the road ahead is well lit. The recent introduction of LED-based lighting for autos is set to improve driver safety and comfort at night, as well as during the day, and offer additional advantages in cabin lighting. Moreover, international standards will play a key role in the move to solid-state lighting (SSL) in the auto.
The need for drivers to see other vehicles — and to be seen by them — after dark emerged naturally as soon as cars first appeared on roads. Lighting had been present on horse-drawn vehicles for a long time because of the same requirement. Initially, in the 1880s, cars were fitted with acetylene and oil lamps. Vehicular lighting had begun a long evolutionary journey.
Early car electrical systems were rather unstable and the lamps were subjected to harsh conditions, such as shock and widely varying climatic conditions and temperatures. All of these contributed to the somewhat slow large-scale implementation of electric lamps, which started only in the 1920s. Other lamps besides headlamps and tail lights have been introduced gradually to meet additional needs. They include fog lamps and various kinds of signalling lamps such as indicators and brake, emergency, parking, and reverse lights.
Slow initial progress
Because the ability to see ahead properly is fundamental to safe night driving, improving the performance of headlamp lightbulbs has always been seen as essential. Until the introduction of high-intensity discharge (HID) lamps, also known as xenon lamps, the light source used in incandescent headlamps was a tungsten filament placed in a vacuum or inert-gas atmosphere inside a bulb or a sealed unit. The main drawback of tungsten bulbs is that their luminous flux (intensity) drops significantly after some 1,000 hours. The tungsten bulbs were further improved with the introduction of halogen gas in the bulbs in the early 1960s. Halogen bulbs had a higher luminous flux and longer useful lifetime.
Xenon lamps that generate light based on the principle of gas discharge were first fitted to motor vehicles in the early 1990s. The xenon lamps represented a major improvement over halogen lamps as their color temperature is closer to daylight, they are brighter, they have a greater range, they better illuminate the edges of the road, and they last at least twice as long as prior lamps. The main drawback to xenon is glare, which can be reduced by various automatic devices. In spite of their qualities, they are not as widely adopted as halogen lamps.
The introduction of LED-based automotive lighting is a relatively recent development. The first LED rear lights and headlamps were fitted to production vehicles in 2003 and 2006, respectively. The benefits of LEDs, especially for headlamps, are already obvious, including the fact that their light color is very similar to daylight. LED headlamps are now being introduced by all major car manufacturers and are seen as the future of automotive lighting.
Besides headlamps, LED-based lights can be used for general and interior lighting. Their higher energy efficiency translates into lower fuel consumption and noxious emissions, helping manufacturers meet ever more stringent regional or national limits. LED light sources have a much longer lifetime that can outlast that of the vehicle. They also offer an unprecedented level of design versatility that is essential for manufacturers, allowing them to differentiate their vehicles from the competition.
International regulations and standards
Road vehicles are produced and traded globally and are used regularly across national borders. The need for international standards is clear as road safety requires that lights are standardized in terms of characteristics such as performance, color durability, and interchangeability.
The UNECE (UN Economic Commission for Europe; www.unece.org) is the international body that sets many of the regulations for road vehicles through its World Forum for Harmonization of Vehicle Regulations (WP 29).
The UNECE Working Party on Lighting and Light-Signalling (GRE) is the subsidiary body that prepares regulatory proposals on active safety for vehicle lighting and light signalling. This group conducts research and analysis to develop lighting requirements for vehicles. Most countries — with the notable exception of the US and Canada, which have their own directives — recognize the UNECE Regulations and apply them in their own national requirements. Much of the GRE's work depends on and references various International Standards on lighting for road vehicles prepared by the International Electrotechnical Commission (IEC; www.iec.ch).
The relatively recent introduction of LED-based light sources has led to changes in standards regulating lighting requirements. Initially fitted to the high-end/luxury segment of the car market, LED lights are rapidly spreading to all categories of vehicles due to their countless benefits and flexibility. As these lights represent a completely new concept, they require new standards to ensure they meet road safety regulations and operate properly in a very demanding environment.
IEC Subcommittee 34A: Lamps prepares international standards for all types of lamps (filament, discharge, or LED), for general lighting and for road vehicles. These standards identify their dimensional, electrical, and luminous requirements as well as their performance requirements.
Lamps for road vehicles are submitted to a particularly harsh environment and since they have a direct impact on road safety, tests are essential to ensure they meet all the necessary requirements.
Differing requirements
The basic function and interchangeability of filament and discharge lamps for road vehicles differ from those of LED light sources. The former types must comply with the IEC 60809 International Standard that defines the dimensional, electrical, and luminous requirements of lamps for road vehicles. In particular, this standard defines the markings, bulbs, dimensions, colors, caps, and bases.
LED light sources, which are based on modules (LED components used by the industry), are not covered by IEC 60809 but by other IEC standards specific to LED modules. However, another International Standard, IEC 60810, which sets out the performance requirements of lamps for road vehicles, applies to the three types of lamps.
LED light sources must meet conditions that do not necessarily apply to filament and discharge lamps, in regard to UV radiation, color maintenance, and electromagnetic compatibility. As LED light sources have a longer rated lifetime than filament or discharge lamps, their lumen maintenance is assessed differently.
Another issue that manufacturers have had to deal with is thermal management, and LED modules and light sources often come with integrated heat sinks. Unlike their filament and discharge counterparts, LED light sources are mainly of the non-replaceable type and are usually intended as components for integration into the luminaire or lighting device by manufacturers. They are designed and meant to be indivisible parts of a lighting or light signaling device, or to be elements of a module or light engine. The auto industry has developed replaceable LED modular sources, usually intended for sale to the general public as a replacement part.
Unparalleled flexibility and benefits
LED light sources can replace all other types of automotive lamps. They are available for headlamps (high and low beam), brake lights, rear combination lamps, center high-mount stop lamps, daytime running lamps (DRLs), turn signals, interior reading lights (map lights), dome lights, accent lights, fog lamps, and position and marker lamps. Moreover, LEDs are being used for ambient lighting and in dashboard and instrument lighting.
In addition to enhanced driving safety and comfort, LED light sources offer many other benefits:
- Lighting flexibility: Lighting requirements and limitations vary greatly according to traffic conditions. LED lighting solutions allow the optimal use of environmental and traffic-related dynamically controllable light distribution patterns such as dynamic bending of light or adaptive front lighting systems (AFSs), already used for other types of automotive lamps. Such adaptive lighting is particularly important to avoid blinding other drivers when crossing or following other vehicles, especially in curves, or to better see fixed or moving obstacles on road sides. LED lighting sources are also dimmable.
- Durability and efficiency: LEDs for automotive lighting have a much longer rated lifetime and use less energy than filament or discharge lamps. LEDs are up to 40% more energy efficient than the former sources. Since less energy for lighting translates into lower fuel consumption, this is a significant feature at a time when tighter consumption and emission rules are introduced in all countries even though road vehicles are required now to use DRLs.
- Design flexibility: A very important benefit of LED lighting solutions for car manufacturers is the design flexibility they offer. Car design bureaus have much greater freedom to come up with innovative designs using lighting to accentuate or attenuate certain shapes and give cars a common brand signature. LEDs were first fitted to vehicles from the exclusive segment of the market, but they are found now in all classes of cars.
Potential not exhausted
LEDs for automotive or other applications are constantly evolving. Their potential in the automotive sector is set to expand as LED modules improve and with the introduction of new technologies such as OLEDs (organic LEDs), which produce a comfortable and homogenous light.
Night driving does not depend only on good vehicle lighting but also on superior road signage and lighting. LEDs are also increasingly showing the way in this very significant area. More benefits of LED lighting have yet to been discovered and it can be safely assumed that they will have a bright future in the road traffic environment.
