How to design a safe, beautiful and practical automotive lighting system

The need to deliver complex styling while meeting vehicle-specific requirements and region-specific regulations has increased the complexity of the optical design process. This has led to an increased reliance on automotive lighting design software to find innovative solutions. High-end simulation software plays an important role in the development of such optical systems as it enables designers and optical engineers to create, simulate and validate optical models throughout the development process - from optical concepts that verify the feasibility of the design all the way to a complete, highly refined and validated product. In addition to a variety of photometric data that characterizes the optical performance, realistic images are used to accurately predict how the lights will look in real life. All of these tasks can be performed virtually in the software, reducing the need for expensive 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 portfolio of optical solutions can help.

Defining automotive interior lighting

Starting with the lighting that the driver and passengers see inside the vehicle, automotive interior lighting is generally divided into the following categories: displays and indicators, interior functional lighting, and accent lighting. The first category of lights allows the driver to get information, which may be standard information displayed on the dashboard, such as range, mileage, or more (think directions on a GPS, menu-driven displays, or light projections from a head-up display, or HUD).

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

The second category is interior lighting, which provides illumination to allow the driver or passengers to see something else. Classic examples of interior lighting systems are dome lights, mirror lights to illuminate the face, map and reading lights, storage lights, etc. The key design considerations for these light sources are precise spatial light distribution to accomplish the specific lighting task, adequate illumination levels and uniformity, all without causing glare. A secondary metric is color, which is used for visibility and mood lighting.

Finally, accent lighting provides styling cues and helps personalize the ambience of a car's interior. It also helps drivers and passengers find controls and features when the cabin is darkened, such as power window controls, radio buttons, and cup holders. Compared to interior lighting, accent lighting typically uses lower lighting levels because its purpose is simply to be visible itself, not to illuminate other objects in the vehicle. For these systems, the main metrics that designers need to keep in mind are color, visual uniformity, and proper light levels.

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 used in this type of lighting are developed to meet several key safety goals, including illuminating the roadway to help drivers identify obstacles and traffic signs in low-light and nighttime driving conditions, optimizing the vehicle's visibility to other drivers and pedestrians, and communicating your intention to turn or slow down to other drivers. In addition to its functional aspects, exterior lighting has evolved into an integral styling and vehicle branding element.

Headlight

Front exterior lighting (called headlights) includes low beam (through beam), high beam (driving beam) and front fog headlights. These lights function to enable vehicles to drive safely at night and in low visibility. They illuminate the road ahead and provide adequate visibility for the driver.

Low beams are useful for nighttime driving in normal traffic to illuminate the road as well as for left and right traffic. They utilize a cutoff line in the beam pattern to prevent glare from other motorists.

High beams provide the greatest coverage for the headlight function and create the best possible driver visibility at night, which is necessary for safe vehicle operation, especially at highway speeds. To this end, high beams do not use a cutoff line.

Since high beams cause noticeable glare for other drivers, they must be deactivated depending on the traffic situation. As an automated solution to this problem, so-called adaptive driving beams (ADB) or pixel light systems are becoming increasingly popular. These sophisticated headlight systems provide situation-dependent road illumination while minimizing glare for other drivers.

Signal lighting

Signal lights include daytime running lights (DRLs), turn indicators, and front position lights within the headlamps. At the rear of the vehicle, signal lights typically include rear position lights (tail lights), brake lights, rear turn indicators, rear fog lights, and center high mounted stop lights (CHMSLs). Along the sides of the vehicle, there may be side turn indicators (on the fenders or mirrors) and/or side marker lights.

These lights are designed to signal actions, such as turning or braking, so that other drivers can recognize your intentions and react accordingly. The placement of the signal lights can also help other drivers understand the size of the vehicle driving behind them.

Light guides have been widely used in signal lighting applications in various design concepts, as the styling opportunities for DRL, turn indicator and tail light functions are almost unlimited. Light guides are also attractive due to their compact form factor, support for flexible light source positioning and overall packaging.

Advances in optical design and simulation software, along with improvements in injection molding tool capabilities, are enabling truly remarkable styling in signal lighting design.

Because the photometric requirements of these light distributions are often easier to meet than headlamps, signal lamps offer more styling opportunities. To accurately predict the aesthetic of these components, designers use photorealistic visualization to simulate their illuminated and unilluminated appearance. Physics-based simulation is essential to achieve the realistic quality required for optical engineering decisions. When designers can develop, test, and validate accurate virtual prototypes, product development time and costs can be greatly reduced.

Additional dedicated vehicle lighting

In addition to front and signal lights, you may also see specialty lights on vehicles—such as license plate lights, which make it easy for other drivers and law enforcement to see the license plate at night or when weather conditions make visibility challenging. In addition, you may see signature lights on the interior and exterior of vehicles, such as illuminated logos for OEM brands.

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

Other lights not used on civilian vehicles but important to commercial, government or emergency vehicles include yellow lights used for hazardous transport warnings; blue lights on fire trucks, police cars and ambulances; flashing lights on road maintenance vehicles; and lights to indicate extended-size vehicles.

Other types of exterior lighting features include welcome lights that provide light as you approach the vehicle, puddle lights on the doors, and follow-home lights that provide illumination to help you walk safely to the front door.

Develop automotive lighting products

Designers and optical engineers must keep many factors in mind when designing indoor and outdoor lighting products. To obtain accurate simulation results, they need precise material and media characterization, including light scattering, dispersion, and absorption effects. To verify all optical requirements, they use Monte Carlo ray tracing methods that allow them to quantitatively predict the specific light distribution of the lamp. Based on the simulation results, they need to check a large number of indicators to evaluate compliance with the requirements. Given the complexity of the analysis and the many design iterations required for most products, engineers must have specialized tools to efficiently extract the required information and evaluations.

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

Simulation of a low-light projector module in LucidShape CAA V5-based software, showing stray light paths caused by reflections from the outer lens and frame

The figure below shows a typical test point analysis of the low beam distribution produced by the Monte Carlo simulation.

Analyzing Regulatory Compliance of Low Beam Distribution in LucidShape Software

Automotive Lighting Design Tools

Automotive lighting products cover a wide range of applications, and the design needs of optical engineers depend on these details. Synopsys offers a broad set of dedicated tools to meet these needs across its optical solutions portfolio, including LucidShape, LucidShape CAA V5 Based, and LightTools software.

The design module in LucidShape CAA simplifies the design process by allowing automotive lighting engineers and designers to create functional geometry based on lighting design standards and complex freeform surfaces based on these and other specifications. These capabilities provide the fine control needed to create superior optical designs that exhibit optimal efficiency, optical performance, and styling flexibility, as well as robustness to tolerances.