Dr. Frank Thim, Brandenburg GmbH
The LED is driving a fundamental technological change in the lighting industry, and automotive lighting is no exception. Using LEDs in exterior automotive lighting provides product differentiation, longer life and lower maintenance costs. The challenge lies in the design.
Figure 1. This side view shows an LED concentrator with a reflector and an aspherical lens (a). An LED concentrator with either a reflector or a primary lens optic is designed to concentrate the light. The light source in this example consists of five LEDs. The corresponding light intensity distribution is shown in (b), with red indicating a higher intensity and blue indicating lower. The light intensity distribution is obtained using a candela sensor, i.e., the luminous intensity in candelas is plotted as a function of horizontal and vertical spread angle in degrees (shown on the X and Y axes, respectively).
In the past, bringing automotive lighting from concept to surface model manually was a complex and laborious undertaking. As a result, automobile manufacturers turned to outside design firms. But Volkswagen of Wolfsburg, Germany, wanted to have greater control over its lighting design, so decided to bring part of it in-house. Today’s illumination design software enabled the manufacturer to do so.
Illumination design programs streamline the concept phase of new car projects. The in-house design team at Volkswagen uses LucidShape illumination design software from Brandenburg GmbH of Paderborn, Germany, to develop design concepts for reflectors and to work out lens geometries. According to Alexander von Hoffman, head of surface modelling and simulation at Volkswagen, the software enables the team to move from a surface model in the design stage to a first virtual light sample within a week, saving time and reducing costs.
Figure 2. A model of an LED disk emitter and a rectangular lens with Fresnel steps is shown in (a). The LED is inside the lens. The corresponding light intensity distribution obtained with a candela sensor is plotted as a function of angle (b). The red rectangle indicates a uniform luminous intensity to a certain angle in both directions.
The company models the LED as an extended source using externally and internally acquired measured ray data files and the company-owned near-field goniometer. The illumination design software reads these measured ray files. In addition, the software contains a library of LEDs from major manufacturers and enables the creation of user-defined LED point light sources. Various surface design concepts for the creation of user-defined reflectors and refractors also are included in the software: procedural surfaces, polycurve systems and macrofocal concepts. The macrofocal concept takes the extended light sources into account and supports complex light functions — such as a sharp edge — in the resulting intensity distribution. Therefore, low, high and signal beam patterns all can be investigated and analyzed.
One of the main challenges of using LEDs is designing a lens and a reflector shape that will create a light pattern that meets US and European regulations. To achieve these goals, Volkswagen utilizes the design software to model various assembly concepts and thereby explore which one works best for a particular application. For example, designers can put the LED inside a reflector, behind a lens, or model a lens/reflector combination. As an option, the LED can have a primary optic directly above its emission area. Various lighting regulations and design concepts require different assembly designs and light intensity distributions (Figures 1 and 2).
Future developments within the lighting and optical design communities will be closely tied to LEDs and simulation software. Illumination design software can reduce new product development costs and save valuable engineering time, while offering immediate and interactive visual and quantitative feedback to a designer.
Contact: Dr. Frank Thim, Brandenburg GmbH, Paderborn, Germany; +49 5251 681 644; e-mail: firstname.lastname@example.org.