LED headlights
LED headlamps are headlamps in which light emitting diodes (abbreviated to LEDs. E. Light-emitting diodes , English light emitting diode ) are used as light sources.
Working principle
LEDs are light-emitting semiconductor components. If electrical current flows through the diode in the forward direction, it emits light, infrared radiation or ultraviolet radiation. The wavelength of the light depends on the semiconductor material and the doping . Compared to incandescent lamps , electrical energy is converted into light with relatively little heat loss . Light is emitted in a very narrow band, so that single-color LEDs often shine red, green and blue. To generate broadband or white light, LEDs of different colors can either overlay their color spectra or single-color LEDs are combined with photoluminescent dye. This means that short-wave, higher-energy light such as the blue light of the LED can be converted into long-wave light. The choice of phosphors can vary and determines the color temperature of the emitted light. Since individual, smaller LEDs have a low luminous flux compared to incandescent or xenon gas discharge lamps , several LEDs are usually bundled together in so-called LED modules. Each LED can be provided with its own bundling optics or a common optic can be used for the entire module.
construction
The LEDs are combined in the headlight with various optics to generate focused light. For bundling, lenses , parabolic mirrors or various combinations thereof can be used for each individual LED or for entire modules. The individual radiation characteristics are averaged with their errors (alignment and radiation angle) to form the overall directional effect, which, however, has so far been far lower than that achievable with incandescent lamps or gas discharge lamps (high-pressure short-arc lamps). Thermal management is necessary for larger LED headlights, as LEDs are sensitive to temperature due to their structure. Simple heat sinks are often used to ensure sufficient cooling. The housing or the device carrier can also be used as a heat sink. The LEDs are connected in series in smaller groups and these in turn are connected in parallel to form a matrix ( array ) and are supplied with protective circuits from a constant current source. With direct current, the power source consists in the simplest case of a resistor, with larger headlights an electronic circuit or a switching regulator . If alternating current is used, electronic ballasts are necessary, which in the simplest case consist of a miniature transformer , ballast capacitor , a rectifier and a smoothing capacitor.
In the case of higher-quality headlights, the electronics enable many functions, such as luminous flux tracking to prevent degradation of the LED, brightness control and, in the case of multi-colored headlights, the continuous change of the light color through additive color mixing of LEDs with the primary colors red, green and blue.
commitment
LED headlights are increasingly replacing other headlights because they age more slowly, have less heat loss and, compared to incandescent lamps, require less energy for the same luminous flux. LED spotlights are used in effect lighting, light shows, stages and discos in combination with lighting controls . Color change mechanisms or color filters are no longer necessary. Operating lights also use LEDs. Light microscopy uses small LED emitters. Small LED headlights are increasingly replacing halogen cold-light mirror lamps for mains operation and for operation on a 12-volt mains transformer, as is also used for low-voltage halogen systems. Ring-shaped lights made of many self-bundling white or single-color LEDs are used for object recognition in automation technology.
Infrared LED spotlights are used to protect property using surveillance cameras.
lifespan
Individual LEDs have a lifespan of up to 100,000 hours, depending on the manufacturer. The information always relates to the decrease in luminous flux of the LED so that it can be operated without any problems over its specified service life. The efficiency and thus the light yield decrease. The upstream electronics are also exposed to the same environmental conditions and age as well. The service life of the LED is strongly dependent on temperature. LEDs in light sources are often operated at temperatures above 74 ° Celsius, which reduces their service life to 15,000 to 45,000 hours.
In the AC network, rectifiers and constant-current buck converters are used to keep them in an optimal operating state with low losses.
LED headlights on vehicles
In vehicle lighting , LED headlights are technically possible and are becoming more and more popular. For a long time the LEDs were too weak and the geometry of the light cone ( dipped beam ) caused difficulties. Adaptive LED headlights, which offer advantages over conventional headlights, are now also being used, especially in passenger cars.
The lighting geometry and the functions are implemented with mirrors or lenses . Due to the fast controllability of many individual LEDs, moving parts can often be dispensed with.
A car halogen light bulb with 55 W generates a luminous flux of approx. 1,200 to 1,500 lumens, an LED lamp reaches up to 3,000 lumens.
Passenger cars
history
In 1992, LEDs were used for the third brake light .
In 1998, the first combination rear lights came on the market, in which the rear lights, indicators and brake lights were taken over by LEDs ( Maserati 3200 GT ).
Since the 2000s, LEDs have been widely used in rear lights as taillights, brake lights, parking lights and indicators.
It was not until 2003 that the Hella company presented the first full LED main headlight at the IAA in Frankfurt am Main that met the lighting requirements of the legislature.
In 2005, Hella presented an LED headlight that achieves the same light output as a xenon headlight with the low beam. The so-stocked Golf V - prototype showed that the technical possibilities for full-LED headlights were available.
At the end of 2006, Audi / Automotive Lighting presented the Audi R8 with optional full LED headlights with integrated indicators, position lights and daytime running lights, available from summer 2008. The Lexus LS 600h also had LED low beam as standard and was available from summer 2007.
Daimler's Mercedes-Benz C 218 had the so-called Intelligent Light System as an option. Adaptive LED headlights have been available in the Audi A6 (here called Adaptive Forward Lighting ), in the BMW F12 , in BMW since 2011 ; from 2012 Rolls-Royce (BMW) was the first manufacturer to offer an entire series with (full) LEDs as standard -Equipped with headlights.
2015 Opel introduces a full LED matrix lighting system in the compact class when the first manufacturer Opel Astra K a.
Electrically controlled LED headlights
Electrically controlled LED headlights were introduced at the end of 2013: a headlight consists of several LED modules, some of which can be controlled separately, so that the lane can be automatically illuminated with adapted light distribution and light range without dazzling oncoming traffic. The headlights are controlled by a camera mounted behind the windshield. Control units generate the lighting geometry from this. The active cornering light can therefore work with foresight. A so-called roundabout light can use data from the navigation device to detect roundabouts and adjust the light cone accordingly. Examples: Audi Matrix LED., Mercedes-Benz Multibeam-LED from 2014.
Since 2012, full-LED headlights have also increasingly been offered as special equipment in the compact class such as the Seat Leon III , Audi A3 8V or Opel Astra K.
Market share
Despite the new possibilities in the field of LED technology - for example in design - the xenon light introduced in 1991 (with 38%) and halogen headlights in 2016 continued to have a high proportion of new registrations. In addition to reducing the thermal power loss of the high-performance LEDs, manufacturers are working on solutions without active cooling.
Replacing the widespread halogen lamps in car headlights with LED retrofits is prohibited in Europe. In 2017, an ADAC study showed many advantages - especially for road safety. LED models from Osram, Philips, Nighteye and Ring were tested in H4 / H7 headlights.
motorcycles
Starting in March 2011, LEDs with passive heat sinks were used in an auxiliary headlight for the first time on a motorcycle, the BMW R 1200 GS (K25) and the BMW K 1600 GT . Since model year 2013, BMW has for the first time included a main headlight with LED in the list of options in the BMW R 1200 GS (K50) . This headlight is actively cooled by means of a fan. Since 2017, the passively cooled J. W. Speaker headlight has been offering adaptive cornering lights for motorcycles using position sensors. From 2015, full-LED headlights gradually came onto the market for motorcycles as well. a. in the Honda CRF 1000L Africa Twin, Multistrada 1200 and BMW R 1250 GS. Among other things, the legislator prescribes non-replaceable LEDs in a bonded housing. They must be tamper-proof according to ECE regulation R 87.
Railway vehicles
The locomotive 101 047 was equipped with LED signal lights and a signal light heater in December 2009. This test vehicle is to be used to test whether the conversion is economical for all locomotives of this series. The UIC headlights in LED technology are already known from other series and are equipped with warm white LEDs in the 101 series , which represent the current state of LED technology . What is new is the use of LEDs for the high beam headlights, which is being used for the first time in rail vehicle technology. This locomotive was equipped with a temperature-controlled signal light heater so that the signal lights remain visible even when it is snowing and ice forms. The different lighting regulations in the EU make it necessary to be able to generate the greatest possible number of colors and brightnesses for cross-border multi-system vehicles in a limited space. Many different colored LEDs can be accommodated and also dimmed on one circuit board. This is z. B. used with the Siemens ES64F4 .
Other locomotives equipped with LED headlights are the ÖBB 1144 and the new Mariazeller Bahn “Die Himmelstreppe”.
Cycles
LEDs were initially used on bicycle headlights in addition to the incandescent lamp for the parking light. LED headlights for bicycle lighting have been available since 2007 . This was made possible by the availability of white LEDs with a power of 3 W. With them, the light output is higher than that of good halogen headlights. Most bicycle LED headlights use a free-form reflector to shape the light distribution.
Bicycle headlights with rotationally symmetrical optics are unsuitable for road traffic and are mainly used on mountain bikes .
Parking lights and daytime running lights
With many LED headlights, the headlight LED also takes on the function of a parking light. If the dynamo does not supply any energy, the LED is fed for a few minutes by a double-layer capacitor which is charged while driving; the parking light has a significantly reduced brightness. Some LED headlights have an additional LED for a daytime running light, which has a different brightness than the nighttime running light.
Legal requirements
The legal requirements in Germany are regulated by StVZO § 67 and TA 23 . Since 2006, the light output in the core lighting area must be at least 10 lux . The light distribution is also specified in TA 23. It should ensure good illumination of the roadway without dazzling oncoming traffic. The electrical power of approved lighting systems must be at least 3 W, with 2.4 W attributable to the front light (TA 4, Paragraph 13). The common hub or side dynamos have an output of 3 W at 0.5 amps; 6 volts.
LED headlights in sports facilities
Since 2014, LED floodlight systems have also been increasingly used on municipal sports facilities. The floodlight system of the Allianz Arena in Munich consisted of metal halide lamps until summer 2017 and was modernized with LED spotlights. The higher investment costs compared to high pressure sodium lamps are offset by lower operating and maintenance costs. The investment costs for a floodlight system with metal halide lamps for a football field with floodlights of lighting class III are around 57,000 euros, an installation with LED floodlights is around 30,000 euros more expensive and is 87,000 euros. In a floodlight system in German stadiums, LED floodlight systems are currently rarely found - unlike in the English Premier League, for example.
Advantages and disadvantages of LED headlights
advantages
- long operating time (up to approx. 50,000 hours, no total failure)
- high energy efficiency
- high mechanical robustness
- different, efficiently generated light colors without filters possible
- extended design options due to low heat loss
- instant switching on and off
- no loss of service life due to frequent switching on and off
- very little ultraviolet and no infrared is produced
- high efficiency in partial load operation (slightly higher efficiency than at full load)
- LED headlights do not require protective glasses to protect against flying glass fragments.
disadvantage
- LED headlights have a higher acquisition cost compared to other headlights. One reason for this is the technologically complex production of the LED
- The heat loss is difficult to dissipate with LED headlights. The temperature in the LED crystal must not exceed about 150 ° C. For this reason, a large heat sink , sometimes with active cooling (fan), is necessary for outdoor lights and high ambient temperatures .
- With the same luminous flux, LED headlights have a larger housing than incandescent or gas discharge lamps because of the cooling.
- The efficiency and also the service life of LEDs decrease with increasing temperature.
- The series connection of the LEDs results in an increased risk of failure of the entire string.
See also
literature
- Roland Lachmayer, Mirco Götz, Michael Kleinkes, Wolfgang Pohlmann: LED technology in headlights - new possibilities with light-emitting diodes. In: ATZ. Automotive magazine. Vol. 108, No. 11, 2006, ISSN 0001-2785 , pp. 956-961, doi: 10.1007 / BF03221836 .
- Karsten Eichhorn, Mirco Götz, Andreas Himmler, Jacek Roslak: Active light - innovative approaches for the next generation of headlights . In: ATZ. Automotive magazine. Vol. 107, No. 11, 2005, pp. 978-983, doi: 10.1007 / BF03223508 .
- LEDs MAGAZINE, June 2006
Web links
- Information and videos from Hella on various headlamp light sources
- LED spotlights in event technology and acceptance in art ( Memento from May 4, 2011 in the Internet Archive ), hbernstaedt.de, archived from the original
- Beam angle with LED lamps and their meaning , ledroom.de blog 2011, archived from the original
Individual evidence
- ↑ Jürgen Gausemeier, Klaus Feldmann (Ed.): Integrative development of spatial electronic assemblies. Hanser Fachbuchverlag, Munich a. a. 2006, ISBN 3-446-40467-8 , p. 40.
- ↑ Hellmuth Nordwig: Phosphors for the white LED in dradio “ Research News ” from December 4, 2013
- ↑ LED headlights: dazzling prospects Die Zeit, on December 13, 2017
- ↑ Maserati 3200GT Boomerang Taillights (1998). In: cardesignnews.com. November 8, 2017, accessed on March 22, 2018 (English): “Affectionately known as the 'boomerang' lights, the taillights were not only an unusual shape, but also included one of the first major uses of LED technology. [...] Set out across the rear quarter panel and boot lid, the outer section of taillight housed the LEDs and made up the tail lamps, brake lamps and indicators. "
- ↑ Opel LED matrix light Intellilux ( Memento from March 4, 2016 in the Internet Archive )
- ↑ New Mercedes-Benz CLS with multibeam LED technology ( Memento from December 5, 2014 in the Internet Archive ) auto-fokus.com, June 17, 2014
- ↑ Audi A8 shines in a new light ( Memento from January 9, 2015 in the Internet Archive )
- ↑ ( Page no longer available , search in web archives: media.daimler.com/dcmedia/0-921-1708962-49-1712129-1-0-0-0-0-0-0-0-0-1-0 -0-0-0-0.html )
- ↑ DAT-Report 2016. Deutsche Automobil Treuhand, January 27, 2016, accessed on April 15, 2019 .
- ↑ In: Automobile Production. No. 7–8, 2011, p. 54.
- ↑ ADAC study on retrofitting with LED lamps focus.de, on December 16, 2017, accessed on April 12, 2019
- ↑ TFL legal, LED on the advance, Xenon: skipped motorradreisefuehrer.de, on March 13, 2019
- ↑ In: DB Bahn - Tf Aktuell. December 26, 2009, p. 2.
- ↑ What does a floodlight system cost? | Sports facility calculator. In: sportstaettenrechner.de. Retrieved October 4, 2016 .