Valeo has been an automotive lighting leader for years. The company delivers its solutions both to first line assembly, as well as for the aftermarket. Valeo experts are always ready to technically support all market players. Today, they’ve prepared a short explanation of two, still most popular automotive lighting solutions: halogen and xenon headlamps.
Halogen and xenon headlamps – basic information
The halogen lighting technology has been used since 1950s. Since that time this technology has been constantly improved, however its basic assumptions remain unchanged.
Halogen technology is a significant improvement in comparison to traditional incandescent headlamps. Halogen headlamps are characterised by longer lifetime due to the resistance to loss of transparency of the light bulb. The combination of halogen gas and tungsten filament allows for the regeneration process which redeposits the evaporated tungsten to the filament. This increases the life and maintains the clarity of the envelope, improving the luminous efficacy.
Owing to the reaction the halogen lamps retain their initial properties for the whole lifetime
Gas discharge lamps of high intensity used in the automotive sector are called xenon headlamps. In practice these are a combination of metal and halogen lamps filled with xenon gas. It’s an optimal solution when one takes into consideration the ratio of effects to production costs. The first gas discharge lamp solution was used in a stock car in 1991. The basic advantage of this solution is the colour of the light that closely mimics the sunlight. The reaction undergoing in this type of headlamps is totally different from the one going on in the halogen lightbulbs. There’s no filament and the light is produced by an electric arc in a glass arc tube. The xenon arc tube is placed between two electrodes in a quartz lightbulb filled with a mixture of noble gases and metal halides. The properties of discharge lamps are dependent on the gas pressure as well as the frequency of electric impulses. Such lamps are filled with such noble gases as: argon, neon, krypton, xenon or their mixtures. Each gas, depending on its atomic structure, emits specific in length waves resulting in various colours of the produced light.
Comparison of halogen and xenon headlamps
When compared to halogen headlamps, discharge lamps are characterised by better intensity and light distribution, as well as higher durability. They are, however, a more complex system containing many elements, which increases their production costs.
Type-approval standard ECE R99 defines the colour tolerance for xenon lamps on a chromaticity diagram. The aim is to obtain the value of 0.375 on both x and y axes. The tolerance range displayed on the diagram corresponds to the range between 4000K and 5000K. In case of halogen headlamps the tolerance range places between 3000K and 3550K.
Lower temperatures of colours indicate a higher degree of red casting and higher temperatures indicate the casting of blue. Halogen high beam is reddish, while xenon is bluish.
Lighting of the future?
Despite the lower durability of the bulbs halogen headlamps are deemed to be a solution easier in production and usage.
When it comes to xenon headlamps, apart from the complexity issue described above, the problem is that they emit diffused light when dirty, which blinds the approaching drivers. This is not only the case when we talk of xenon headlamps, but the diffusion effect in their case may be more evident and may endanger road safety. This pertains mainly to the older-type xenon lamps, the stream of light of which is higher than 2000lm. That’s why European cars equipped with such systems need a dedicated, high-pressure cleaning so that any diffusion doesn’t affect road safety. This increases the production costs. Recently, there appeared on the market xenon systems with lower stream of light, which do not need any additional cleaning systems. Automotive lighting manufacturers are gradually moving away from xenon technology and turn towards a cheaper and more efficient LED technology. These solutions will be discussed in a separate material.
When it comes to xenon headlamps, apart from the complexity issue described above, the problem is that they emit diffused light when dirty, which blinds the approaching drivers. This is not only the case when we talk of xenon headlamps, but the diffusion effect in their case may be more evident and may endanger road safety. This pertains mainly to the older-type xenon lamps, the stream of light of which is higher than 2000lm. That’s why European cars equipped with such systems need a dedicated, high-pressure cleaning so that any diffusion doesn’t affect road safety. This increases the production costs. Recently, there appeared on the market xenon systems with lower stream of light, which do not need any additional cleaning systems. Automotive lighting manufacturers are gradually moving away from xenon technology and turn towards a cheaper and more efficient LED technology. These solutions will be discussed in a separate material.
