Bright future for LEDs on the roads
Car manufacturers are introducing LED-based lights in all classes of vehicles
Morand Fachot (edited version of article published in LEDs Magazine, July 2013)
IEC International Standards and evolving LED technology will both play a key role in increasing the adoption of solid-state lighting in automotive applications.
Better vision, safer driving in poor visibility
The majority of drivers feel stressed in poor visibility conditions, particularly at night when the ability to perceive and judge distance is severely impaired. Although traffic on the roads is much lighter at night, in many countries, including the US, around 40% or more of all traffic fatalities occur during night-time hours. Well-lit roads ease drivers' strain and greatly increase safety. The recent introduction of LED-based lamps (also called SSL, solid-state lighting) for autos is set to improve driver safety and comfort at night, as well as during the day, and to offer additional advantages in cabin lighting. Moreover, IEC International Standards will play a key role in the move to SSL in automotive lighting, a market whose total value is forecast to grow from nearly 19,5 billion in 2013 to more than USD 25,3 billion by 2018.
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. Initially, cars were fitted with acetylene and oil lamps.
Early car electrical systems were rather unstable and their 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 only started in the 1920s.
Slow initial progress, but rapid expansion now
Because the ability to see ahead properly is fundamental to safe night driving, improving the performance of headlamp light bulbs has always been seen as essential. Until the introduction of HID (high-intensity discharge) 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. They represented a major improvement over halogen lamps as their colour temperature is closer to daylight, they are brighter, they have a greater range, they illuminate the edges of the road better and they last at least twice as long. The main drawback to xenon is glare, which can be reduced by the incorporation of various automatic devices. In spite of their qualities, xenon lamps are not as widely adopted as halogen lamps.
LEDs enter the automotive world
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 colour 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 than their predecessors; they may even outlast the vehicle to which they are fitted. 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, colour 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 IEC.
The relatively recent introduction of LED-based light sources has led to changes in lighting standards. Initially fitted to the high-end/luxury segment of the car market, LED lights are spreading rapidly to all categories of vehicles due to their wide-ranging 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 highly demanding environment.
IEC SC (Subcommittee) 34A: Lamps prepares International Standards for all types of lamps (filament, discharge and LED), for general lighting and for road vehicles. These Standards identify the lamps' dimensional, electrical, luminous and performance requirements. Lamps for road vehicles operate in a particularly harsh environment and since they have a direct impact on road safety, tests are essential to ensure they meet all the necessary conditions.
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, colours, 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, the latest edition (released in February 2013) of another International Standard, IEC 60810, which sets out the performance requirements of lamps for road vehicles, applies to all 3 types of lamps.
LED light sources must meet conditions that are not necessarily relevant to filament and discharge lamps, in terms of UV radiation, colour 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 as, and meant to be, indivisible parts of a lighting or light signalling 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 replacement parts.
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, centre high-mount stop lamps, daytime running lamps (DRLs), indicators, 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 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 turning across or following other vehicles, or for better visibility of fixed or moving obstacles on road sides. LED lights 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 reduced 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 in many countries
Design flexibility: an 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 now found 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 as new technologies like OLEDs (organic LEDs), which produce a comfortable and homogenous light, are introduced. Safer night driving conditions do not depend on good vehicle lighting alone but also on superior road signage and lighting. LEDs are also increasingly showing the way in this highly significant area. Further benefits of LED lighting for automotive applications are likely to be discovered and it can be safely assumed that they will have a bright future in the road traffic environment.