The technology of automotive lighting passed through substantial changes in recent years. Gas discharge lamps, for example, highly extended the features of front lighting systems. Currently, LEDs revolutionize the appearance of rear and front signal lights. The area of interior lighting experiences a trend towards new light sources as well. The new illuminants are combined with new optical components such as light guides, pattern-free cover lenses or free-form reflectors. The challenge for the optical designer is to take advantage of these new design possibilities to improve the optical performance and meet additional customer demands. Daylight and night time appearance, for example, is important for any new design. Especially the individual styling of signal lights guarantees a long term recognition factor. Consequently, the optical design of tail lamps is influenced by an increasing number of styling aspects, which contribute to the special character of the vehicle. The technique is demonstrated by a tail light example. Conventional car signal lamps consist of at least three assembly groups. The bulb holder provides the position of the light source, the housing contains the reflectors and the cover glass usually creates the final light distribution. Other concepts use reflector optics, intermediate lenses, or light guides. It was worked with different concepts to realize the tail light as an example of a thin lamp. First three kinds of coupling optic (CO) to couple the light from the LEDs into the light guide (LG) was analyzed. Design 1: Direct coupling of the LED to the input side of the LG (preferably the upper side) is possible. To handle direct and reflected (TIR) light the geometry of the segments has to be more complex than in designs 2 or 3. Design 2: A tapered rod made from PMMA and working with total internal reflection is a powerful and variable CO because of its high efficiency and its variation in horizontal and vertical angle. The latter is achieved by varying the size and aspect ratio of input and output face of the rod. Design 3: The TIR-optic covers the whole flux from the LED and directs it into a small solid angle. LED driven tail lamps with light guides can be designed as thin lamps with different aspect ratios, even 'three dimensional', thus complying with modern styling demands. They fulfil the regulations for a tail light and a brake light, simultaneously. There is a choice in the type of the coupling optic and, hence, in the type of LED as well. The TIR CO has the greatest potential to improve the system.
Optical design of LED-lamps for automotive applications
Optisches Design von LED-Lampen für automobile Anwendungen
2007
8 Seiten, 4 Bilder, 2 Tabellen, 3 Quellen
Aufsatz (Konferenz)
Englisch
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