Assistance from a virtual world

SIMULATION SOFTWARE HELPS DEVELOP LED APPLICATIONS IN AUTOMOTIVE LIGHTING DESIGN

LEDs have revolutionized lighting technology. The development of automotive backlights exemplifies the latest trends and soon headlamps will also be fitted wih the latest LED technology. Illumination design software helps automotive lighting designers address the challenges posed by LEDs’ unique characteristics.

FRANK THIM WILLI BRANDENBURG

Visualization and simulation of LED systems, such as the automotive headlamp, in the illumination design software like LucidShape, allows users to familiarize themselves with performance of a new light source in a virtual environment. This simulation is a requirement to avoid unnecessary costs associated with expensive fabrication, while also reducing the time to market. Lucid-Shape provides the tools to design faceted and freeform reflectors and lenses utilized in LED applications for external automotive lighting. It also performs an interactive ray trace and provides the tools to analyze the output from automotive lighting models.

Modelling LED light sources

There are three different ways to model an LED source in illumination design software:

• Model the LED as a point light source in angle with the measured intensity distribution.
• Model and simulate the LED, including its geometry, e.g., reflector cup and die, encapsulation, lens, and mounting assemblies, including reflection, refraction, and scattering effects.
• Model the LED as an extended source using externally acquired measured ray files.

The first method is simple, but far less accurate for classical optics design. This method is especially limited in the near field, i.e., the spatial distribution from the LED is not accurately modeled. The second method requires a detailed knowledge about the LED, e.g. the surface properties of the materials which are likely not available from LED manufacturers. The second method takes into account secondary effects, like light blocking and reflection, and therefore is accurate also for near-field optical applications. The third method is the most common approach, which offers accurate solution for most LED applications. All three methods to model LEDs are available in LucidShape. A library of LEDs from major manufacturers is included in the software and LucidShape is capable of reading external ray files.

Reflector and lens design

The desired light pattern in automotive applications are usually demanded by government regulations (ECE and SAE). Therefore, the design of lenses and a reflectors are complex and extensive. There are three different surface design concepts in LucidShape to fit design requirements of various LED applications: ›Procedural Surfaces (PS)‹, ›Poly Curve Systems (PCS)‹ and ›Macrofocal Concept (MF)‹.

One or two curves define the light function in the procedural surface (PS) concept. The surface is then built with a rotation or sweep operation. Surfaces in poly curve systems (PCS) are built through a skeleton of curves. The extended light sources in the macrofocal concept (MF) design are modeled as macrofocal objects.

Overview of LED applications

There are essentially three different techniques for the design of LED-based applications, based on the positions of lens and reflector: LEDs can be used inside of a reflector (R), behind a lens (L) and in combination with a lens and a reflector (L+R). As an option, the LED can also have a primary optic (PO) situated directly above its emission area. All these techniques can be modeling in the software.

LED concentrators are a primary optics application, which can be used either to focus LEDs or to achieve a different mix of colors. There are a number of automotive applications, e.g. signal lamps and lowand high-beam headlamps, where the light distribution is defined in the far field. On the other hand, there are near field automotive lighting applications, e.g. license plate illuminators and interior lighting lamps. Each of the techniques described previously is better suited to certain applications.

Table A provides an overview of the different design techniques utilized in LED applications and includes six different examples a) to e):

• Example (a): An LED concentrator either with a reflector or a primary lens optic is designed to concentrate the light. Figure 1 demonstrates a LED concentrator in side view. The light source consists of five LEDs inside the primary optic (purple), which might be either a reflector or refractor. It is displayed together with an aspherical lens (green.
• Example (b): LED PCS (Poly Curve Systems) is another type of application, which might be used for the creation of automotive headlamps. The reflector is built by different base curves. Figure 2 shows a side view of a PCS system with a half reflector. Again, the aspherical lens is shown in green and the reflector in purple.
• Example (c): Figure 3 presents two LED reflectors. The first one is designed with the procedural operation like rotate or sweep, the second is the macrofocal concept reflector. The resulting beam patterns are also shown.
• Example (d): Figure 4 shows an LED with a lens and the corresponding light intensity distribution. The model consists of an LED disk emitter and a rectangular lens with Fresnel steps.
• Example (e): Figure 5 shows an application using a LED primary optic (LEDPO) with a lens.

Summary: light technique = LEDs + simulation software

Future developments within the lighting and optical design communities are closely connected with LEDs and simulation software. We have demonstrated the potential use of illumination design software on LED application examples. Illumination design software like LucidShape is an ideal tool for a lighting designer or illumination engineer to design LED applications and evaluate the desired beam patterns.

AUTOREN

Dipl.-Phys. Dr. FRANK THIM works as Customer Support, and Dipl.-Informatiker WILLI BRANDENBURG is General Manager at Brandenburg in Paderborn.