How to Design Exterior & Interior Automotive Lighting Systems

The next generation of interior automotive displays may provide a fully digital cockpit that can be customized by the driver. Key characteristics for display and indicator lighting are color, luminance, and luminance uniformity.

The second classification, interior illumination, provides lighting that allows the driver or passengers to see something else. Classic examples of interior illumination systems are dome lights, mirror lights that illuminate a face, map and reading lamps, storage lights, and so on. The key design considerations for these lights are precise spatial light distribution to accomplish specific illumination tasks, sufficient illuminance levels, and uniformity, all without causing glare. A secondary metric is color, for both visibility and mood lighting.

Finally, accent lighting offers styling cues and helps to personalize the automotive interior’s ambience. It also assists drivers and passengers in finding controls and features, such as power window controls, radio buttons, and cupholders when the cabin is darkened. Compared to interior illumination, accent lighting generally makes use of lower illumination levels, because its purpose is simply to be visible on its own, not to shed light on other objects in the vehicle. For these systems, the main metrics designers need to keep in mind are color, visual uniformity, and appropriate light levels.

Forward Lighting

Front exterior lighting – known as forward lighting — includes the low-beam headlamp (passing beam), high-beam headlamp (driving beam), and front fog headlamp. These lamp functions make it possible for vehicles to be driven safely at night and when visibility is low. They illuminate the road ahead to achieve adequate visibility for the driver.

Low beams are useful for night driving in normal traffic, illuminating the road and what’s to the left and right. They utilize a cutoff line in the beam pattern to prevent glare for other motorists.

High beams provide the headlight function with the most reach and create the best driver view at night, which is required to safely operate a vehicle, especially when driving at higher speeds. To accomplish this, high beams do not utilize a cutoff line.

Because high beams can produce significant glare for other motorists, high-beam headlights must be deactivated based on the traffic situation. With an automated solution for this problem, so-called adaptive driving beam (ADB) or pixel light systems are becoming increasingly popular. These sophisticated headlight systems can provide situation-dependent road illumination while simultaneously minimizing glare for other motorists.

Signal Lighting

Signal lighting includes the daytime running light (DRL), turn indicator, and front position lamp within headlamps. In the rear of the vehicle, signal lighting typically includes the rear position lamp (tail lamp), stop lamp, rear turn indicator, rear fog lamp, and center high-mounted stop light (CHMSL). And along the sides of a vehicle, there may be side turn indicators (on the fender or side mirror) and/or side marker lights.

These lamps are designed to signal an action, like turning or braking, so that other drivers can recognize your intentions and react accordingly. The placement of signal lamps also helps other drivers get a sense of the dimensions of the vehicle they are driving behind.

Among a variety of design concepts, light guides have been extensively used for signal lighting applications, given the almost limitless styling opportunities for DRL, turn indicators, and tail lamp functions. Light guides are also appealing because of their compact profiles, supporting flexible light source positioning, and overall packaging.

Advancements in optical design and simulation software, along with improved tooling capabilities for injection molding, have led to signal lighting designs that exhibit truly exceptional styling.

Additional Special-Purpose Vehicle Lighting

In addition to the forward and signal lighting, you might see special-purpose lamps on a vehicle — a license plate lamp, for example, which makes the license plate easily visible to other drivers and law enforcement officers at night or when weather conditions make visibility challenging. Additionally, you might see signature lamps, such as illuminated logos of the OEM brand on the interior and exterior of the vehicle.

Vehicle-to-X (V2X) lighting is an emerging type of lighting that is gaining traction with the introduction of autonomous and electric cars, and it provides a light-based visual communication system that signals to pedestrians or other drivers the intentions of a near-silent vehicle or one without a driver. V2X lighting functions are a current topic of research and interest, along with sensor systems (such as cameras, LiDAR, and radar).

Other lamps that aren’t used on civilian vehicles but are important for commercial, government, or emergency vehicles include yellow lamps for hazard transport warnings; blue lamps for fire trucks, police cars, and ambulances; flashing lights on road maintenance vehicles; and lamps that indicate extended size vehicles.

Other types of exterior lighting functions include welcome lights, which provide light as you approach a vehicle, puddle lights on car doors, and follow-me-home lights that provide illumination to help you safely walk to your front door.

Developing Automotive Lighting Products

There are many factors that designers and optical engineers must keep in mind when designing interior and exterior lighting products. To achieve accurate simulation results, they need precise material and media characterizations, including light scatter, dispersion, and absorption effects. To validate all optical requirements, they use Monte Carlo ray tracing methods that allow them to quantitatively predict lamp specific light distributions. With the simulation results, they need to check a multitude of metrics to assess compliance to requirements. Given the complexity of the analyses and the many design iterations most products require, it essential for engineers to have specialized tools for extracting the required information and assessments efficiently.

The following image shows a headlamp model simulated in LucidShape CAA V5 Based, a comprehensive optical design, simulation, and analysis platform developed specifically for the needs of the automotive lighting industry.

The following image shows a typical test point analysis for a low-beam light distribution produced by a Monte Carlo simulation.

Automotive Lighting Design Tools

Automotive lighting products span a wide range of applications, and the optical engineer’s design needs depend on those details. Synopsys offers an extensive set of specialized tools to meet those needs with the Optical Solutions product portfolio, which includes LucidShape, LucidShape CAA V5 Based, and LightTools software.

The Design Module in LucidShape CAA streamlines the design process by allowing automotive lighting engineers and designers to create functional geometry based on lighting design criteria and complex freeform surfaces based on these and other specifications. These features provide the granular control needed to create superior optical designs, exhibiting the best efficiency, optical performance, and styling flexibility, as well as robustness to tolerances.

The following image shows a few of these design features: a reflector and a lens design feature for the low-beam projector module, as well as a design feature for creating sophisticated multi-faceted reflector optics.

LucidShape CAA also features a Visualize Module that allows automotive lighting engineers and designers to create physically correct photorealistic images throughout the product development process to accurately predict how the lighting system is perceived by the human eye. Early in the development process, photorealistic images are used to assess design or material alternatives and whether they meet styling objectives. Once the design concept has been selected, they provide valuable feedback to the optical engineer evolving the design to meet all requirements, and having physically accurate images facilitates targeted design changes. Prior to the design freeze, the product team can review them with the management team, customer, and other stakeholders to ensure that everyone is satisfied the product’s visual appearance, setting clear expectations for the final product.

Acura ILX headlamp CAD model (left) and photorealistic simulation of headlamp with DRL and turn indicator energized (right)

Photorealistic simulation of an Acura ILX headlamp including portions of the vehicle front (left) and tail lamp visualization (right)

LucidShape CAA also offers a Light Guide Design Module to facilitate automotive light guide designs for applications such as daytime running lamps, turn indicators, and tail lamps; this tool enables you to create and optimize light guide systems for uniform appearance and regulation compliance. The Light Guide Designer can significantly reduce the time needed to develop light guides, since highly repetitive manual adjustments to the light guide geometry are automated with its optimization algorithms and can accomplish optical designs superior to expert designs created manually.

              Model of a DRL light guide created with the LucidShape CAA Light Guide Design Module

               Model of a DRL light guide created with the LucidShape CAA Light Guide Design Module

For interior lighting, LightTools illumination design software provides additional design, simulation, and analysis tools for designing superior automotive optical components. The illustration below depicts a display application using a 3D microstructure to achieve uniform illumination across the display.

Automotive lighting is integral to improving driver comfort and safety. Technological advances and engineering ingenuity have led to automotive lighting innovations that were unthinkable even a few years ago. At Synopsys, we see many opportunities to help the industry push the limits even further by providing the tools to solve the engineering problems of tomorrow.