How to Design Exterior & Interior Automotive Lighting Systems

Tobias Schmid

Sep 21, 2022 / 12 min read

Automotive lighting applications have grown in number, variety, and complexity since the early 2000s, significantly enabled or accelerated by the availability of powerful LEDs. From headlights to lights on the instrument cluster and the license plate lamp, vehicle lighting is essential for function, style, safety, and comfort.

The need to meet vehicle-specific requirements concurrently with region-specific regulations and to deliver complex styling has increased the complexity of the optical design processes. This has led to a higher reliance on automotive lighting design software to find innovative solutions. High-end simulation software plays a fundamental role in developing such optical systems because it enables designers and optical engineers to create, simulate, and validate optical models throughout the development process – from optical concepts that verify the design feasibility all the way to a complete, highly refined and validated product. Along with a variety of photometric data characterizing the optical performance, photorealistic images are used to accurately predict how vehicle lights will look in real life. All of these tasks can be carried out virtually in software, which mitigates the need for costly and time-consuming physical prototypes.

Read on to learn more about the types and functions of automotive lighting, the importance of optical modeling and simulation, the different specifications for interior and exterior lights, and how the Synopsys family of optical solutions can help.

Automotive Lighting

Defining Automotive Interior Lighting

Beginning with the lighting seen inside the vehicle by the driver and passengers, automotive interior lighting is typically divided into the following categories: displays and indicators, interior functional illumination, and accent lighting. Lights in the first category allow the driver to acquire information, which could be standard information displayed on a dashboard such as range, mileage, or more multifaceted information (think directions on a GPS, a menu-driven display, or light projection for head-up displays, or HUDs).

Combined HUD Display | Synopsys

                                                                         HUD simulation in LightTools

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.

Digital Vehicle Cockpit | Synopsys

                                                                              Digital vehicle cockpit 

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.

LightTools Map Light Simulation | Synopsys

                                                   Map light simulation in LightTools software

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.

Vehicle Accent LED Lighting | Synopsys

                                                                                 Interior accent lighting

The Purpose of Exterior Lighting

Automotive exterior lighting appears on the front, rear, and sides of a vehicle, and may even extend to the roof. Products for this type of lighting are developed to meet several key safety objectives, including illuminating the road to help the driver recognize obstacles and traffic signs during low-light and night-driving conditions, optimizing the vehicle’s visibility to other drivers and pedestrians, and communicating to other drivers your intention to turn or slow down. Beyond functional aspects, exterior lighting has evolved into an indispensable styling and vehicle branding element.

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.

LucidShape Acura ILX Headlamp Model | Synopsys

                                 Acura ILX headlamp model in LucidShape CAA V5 Based software

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.

                Simulated driver view showing road illumination from a low beam in LucidShape software

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.

LucidShape High Beam Simulation | Synopsys

                    Simulated driver view showing road illumination from a high beam in LucidShape software

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.

LucidDrive Adaptive Front Lighting | Synopsys

                                  Simulation of an adaptive front-lighting system in LucidDrive software

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.

Daytime Running Lights CAD Model | Synopsys

                                                                   CAD model for a DRL light guide

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.

McLaren P1 Tail Lamp Design Simulation | Synopsys

J.W. Speaker McLaren P1 tail lamp design using design and simulation capability in LucidShape. Photo courtesy of McLaren Technology Group

Because photometric regulation requirements tend to be easier to meet for these light distributions than for forward lighting, signal lamps provide more styling opportunities. To accurately predict the aesthetics of these components, designers use photorealistic visualization to simulate their lit and unlit appearance. A physics-based simulation is essential to achieve the photorealistic quality required for reaching optical engineering decisions. When designers can develop, test, and validate accurate virtual prototyping, product development time and costs can be substantially reduced.

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.

LightTools Interior Lighting Simulation | Synopsys

              Interior automotive lighting simulation, including a logo projection, in LightTools software

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.

LucidShape Low Beam Projector Module Simulation | Synopsys

Simulation of a low-beam projector module, showing stray light paths caused by reflections at the outer lens and bezel, in LucidShape CAA V5 Based software

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

LucidShape Regulation Compliance | Synopsys

            Analysis of regulation compliance for a low-beam light distribution in LucidShape software

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 Projector Unit Illumination Simulation | Synopsys

    Illumination simulation of a projector unit and faceted reflectors in LucidShape CAA V5 Based software

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.

Headlight CAD Photorealistic Model | Synopsys

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

Acura ILX Photorealistic Simulations | Synopsys

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

Acura ILX Entire Vehicle Photorealistic Simulation | Synopsys

                                           Photorealistic simulation of the entire Acura ILX vehicle

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

DRL Light Guide Simulation | Synopsys

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

DRL Model Gif | Synopsys

                                   Simulated luminance of a DRL light guide (multi-view animation)

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.

Light Guide Optimization Tool | Synopsys

Display simulation model (left) and 3D textures simulation before and after optimization (right) in LightTools software

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.

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