Lighting

Free-Form Optics for lamp Design By Thomas Weber

The appearance of modern motor vehicles is to a great extent deter ­mined by the design of the lights. However, unusual styling require­ments may stand in the way of optimal lighting efficiency. Thi s dilemma has been solved by H ella's lighting engineers by using the latest free­form technology and new computer algorithms.

1 Introduction

Design is an essential subject especially with regard to the lighting equipment of motor vehicles. Just like "eyes", headlamps cha racterize the vehicle's front view, while combination rea r lamps are a fundamental styling element forthe rear. The customer's decision to buy a certain vehicle is primari­ly influenced by the design of the lighting eqUipment rather than its technical perfor­mance. The reason forthis may be that the increase in safety gained by optimal head­lamps and signal lamps is hardly known to the public. The potential is made dear by a study by Langwieder and Baumler [1) ac­cording to which more than 40% of all fatal accidents happen during the night, al­though night-time traffic volume accounts for only 25% of the total volume of traffic. Although diversity of design is important, it must never mean a compromise with re­gard to traffic safety.

During the development of modern light­ing equipment for motor vehicles, the most diverse requirements have to be taken into account, some of which oppose each other: - superior diversity of design - distinctive appearance both in opera-

tion and when switched off - low cost - high reliability - low energy consumption - small installation depth - optimal visibility (signal lamps) - optimal road illumination without the

risk of dazzling (headlamps).

You Wlr find the rlglJres mentioned il !his article In tile German ISSOO of AT Z 612001 OO:)inlllng Oil page xxx.

Frel-Form-Optlk fOr Deslgn­leuchlen

EspeCially unconventional styling reqUire­ments may stand in the way of optimal technical perlormance. The skill is to devel­op a technically optimal device for unusual design concepts. The key to the solution is the development of specially adapted free­form lamps by means of which the lamp ef­ficiency can be immensely improved. Free­form technology has been used for a long time in headlamps, allowing the construc· tion of headlamps with unstructured clear cover lenses in reflector technology which would otherwise be impossible. In the fol­lowing we will discuss concepts for signal lamps.

2 Free-Form Technology

The optical free-form surlaces do not pos­sess regular geometrical shapes (spherical segments, ellipsoids, etc.) but are exactly adapted to the lighting effect. These free­form surlaces can only be generated with the help of a computer [2). To do this, com­puter algorithms to solve differential equa· tions or generic optimisation procedures (variation procedures, evolutionary proce­dures, etc.) are used. The algorithms can generate optical surfaces on reflectors and lenses [3J. Directly after the calculation of the free-form surlaces, perlormance and lighting patterns are simulated on the com­puter [4J. This reduces development time and cost.

The optical surlaces of signal lamps in most cases consist of a large number of small sur­faces (called optics in the following) with every single one contributing to the total lighting pattern. The consequence is that one sees a multitude of light points when the signal lamp is in operation (at least one from each optic) and the resulting appear· ance is almost homogeneous. Every single optic is automatically optimised on the computer in such a way that it meets the legal requirements with regard to the beam

pattern. The size, number, boundary lines and shape determine the design impres­sion. Requirements such as a special design or a particularly homogeneous luminosity distribution are already taken into account during the calculation. Thus, optimum light distribution is achieved even if unusual contour lines are required.

A number of design samples have been pre­pared on the basis of these new calculation methods which meet the legal require­ments (ECE and SAE), Figure 1. The techni­cal lamp efficiency has been conSiderably improved due tothe application of the new technology, with the result that bulbs that consume less power can be used, Figure 2 and Figure 3, or overall dimensions can be reduced (e.g. back-up light with a diameter of 30 rom). Of course, this kind of free ·form technologycanalso be applied to other illu­minants (e.g. LEOs) and is not restricted to signal lamps, Figure 4.

3 Summary

Extraordinary design concepts with a high recognition value and optimal lighting properties need not be contradictory. The specific use of free-form technology allows the integration of appropriate styling ele­ments without making a compromise with regard to the efficiency of the lighting equipment and thus traffic safety. The complexity of the system associated with the new possibilities does not necessarily lead to higher development costs. On the contrary, computer engineering especially adapted to the product may even shorten the development process.

References [I] K. Langwiffler, H. sawnler, Charakteristik von

Nachtunfallen [Charact eristics of aCCidents at night], Progress in Automobile lighting, 1997

[2] Th. Weber. Von der Lichtstarkeverteilung zur Reflektorgestalt [From Luminous Intensity Di~ tribut ion to the Shape of the Reflector ]. Hella R&D Review, 1996

[3 ] Th. Weber, Free Form Optics for Signal light · ing, Progress in Automobile Ughting . 1999

[4 ] D. Wendt; HEUOS - Das neue Lichtlabor von Hella ]HELIOS- Hella·s New Ught Laboratory]. ATZ, January 1995

[5] Web site: http://WoNW.hella.de/mainde/levlb/ lev2ballev3babllev4babdlindex.htm

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