What is Automotive Interior Lighting?

Vehicles have many types of interior and exterior lighting systems that perform a range of functions — some are for safety, some are for style. The lighting inside a vehicle is known as interior automotive lighting and includes any type of internal illumination that affects the drivers and the passengers, but doesn’t have a bearing on anyone outside of the vehicle.

Interior car lights can display important information, such as the speed and fuel level, or the various warning lights that illuminate when there is a problem (e.g. a low oil level or high engine temperature). These are critical and functional safety lights. Then, you also have stylish lighting that improves passenger comfort, gives the car personality, and serves a functional purpose such as illuminating the door panel. 

With so many different interior lighting systems inside every vehicle, there are many engineering design challenges to overcome before a lighting system is suitable for commercial use.

Interior lighting systems can be split into three main categories, which contain many different types of individual interior lights:

• Display lighting
• Illumination lighting
• Ambient lighting (accent lighting)

Display Lighting

Display lighting relays information to the driver and passengers, such as speed, navigation, and safety information about the engine. Display systems, such as touchscreens, are also found in modern cars in the center of the dashboard, and are used for navigating the radio and Bluetooth settings, app control, coordinating A/C, and controlling other atmospheric functions of the car.. 

Some key examples of display lighting include:

• Dashboard lighting
• Multimedia displays
• Instrument panels
• Satellite navigation

Among the newest display technologies are heads-up displays that are projected onto the windshield and are connected to the cluster of safety lighting components displayed just above the steering wheel. Moving these warning lights up into the drivers eyeline means that drivers don’t need to take their eyes off the road to follow navigation or see which warning lights have illuminated.

Illumination Lighting

Illumination lighting is functional lighting inside the car that helps people to see andfind things inside the vehicle. Common illumination lighting used inside vehicles includes:

• Dome lighting
• Mirror lighting
• Storage lighting
• Trunk lighting
• Map and reading lamps
• Glove box lighting
• Courtesy lighting

Ambient Lighting

Ambient lighting — also known as interior accent lighting — is used to provide styling cues, create an ambiance inside the car, and illuminate different controls around the car. Ambient lighting is not critical for the functionality of the vehicle and tends to have a lower light intensity because it doesn’t need to illuminate other objects inside the vehicle.

Ambient lighting is often located below the belt line of the vehicle and aims to provide a better user experience rather than a safety or functional performance. 

Some examples of ambient lighting applications include:

• Window control lighting
• Lighting around radio knobs and other control knobs
• Footwell lighting
• Door panel lighting
• Lighting up cup holders
• Lighting for charging ports

With so many different types of car interior lights, there are many design considerations that engineers need to think about from a performance and safety perspective. Engineers must also consider the consumer who will be driving the vehicle, as style is often valued more than function. In many cases, a balance needs to be struck between functionality, style, and theme harmonization for all parties to be happy with the finished product.

Small components — such as the needles for the speedometer — look very simple to design, but behind their simplistic appearance are layers of complexity. 

These needles undergo etching, coating, and painting processes to get the desired optical transparency so that light can pass through them. Some contain prisms on the back of the needle as well. These coatings and paints are thin-film layers, so a high degree of precision is required to design and manufacture them. 

The other small graphics on the instrument panel also require the plastic to be etched to a desired transparency so that different colors of light can be emitted through them to the driver.

Picking the Right Colors

Engineers today have different LED options and color combinations available to them, which gives more choice to the consumer. However, cost versus design functionality still needs to be maintained, as more extravagant color systems are more expensive than conventional LED lighting kits.

Graphics on the dashboard or instrument panel are safety warning lights that are critical for ensuring that any issues are resolved immediately. Engineers have access to many types of lighting kits today, so there is a higher degree of customization possible with interior lighting systems. Some examples of lighting options available to engineers include:

• LED strips 
• LED modules
• LED fiber optics
• MicroLEDs
• White LEDs
• Multi-colored/RGB LEDs
• LED bulbs
• Conventional/incandescent light bulbs

Because there are many different colors used — for example, red is urgent and requires immediate attention, and orange is slightly urgent and requires attention soon — those colors need to be uniform and accurate, regardless of which lighting kit is used.

If they are not accurate,  the driver might miss key issues that compromise the safety of the vehicle and those in it. A green “check engine” light doesn’t quite communicate the same urgency as red.

Designing the Packaging Space in Overhead Lamps

Another interior lighting design consideration centers around how the packaging space should be optimized in overhead lamps. The packaging space is the first thing to consider, as it needs to be acceptable from an aesthetic point of view for the driver. However, requirements must still be met around the light output so that any passenger can see inside the car interior when it is turned on. 

Overhead lamps are one of the key design challenges where there must be a trade-off between style and functionality. The design process requires a lot of back and forth between engineering and styling to come to a beneficial design from both angles.

Then there are the different components inside the lamp to consider. For example, the lens might have some graining or  prisms to help propagate and aim the light. The lens might also require a certain level of transparency that needs to be precisely engineered.

The decision also needs to be made around how many LEDs (or light bulbs) are going to be used in the design, as this will affect the functional requirements of the lens and other optical components in the lamp.

Single vs. Multi-LED Design Considerations

Going from one to two LEDs causes a substantial increase in cost and is a design decision that needs to be made early on to account for different design considerations. One example is door panel lights. The curvature and length of the pipe might require multiple LEDs to achieve a uniform light output.

Similarly, the type of LED needs to be considered with cost and functionality in mind, as some LEDs offer multi-color functionalities and lighting effects. RGB LEDs offer more flexibility and freedom to customize the color of the lighting system but are much more expensive than traditional LEDs. In some cases, traditional interior LEDs must be chosen based on the volume of the vehicle being manufactured.

Optimizing the design process with simulation software like Ansys Speos helps to save time and money while streamlining the work. Speos software is a physics-based modeling tool that predicts the illumination and performance of optical systems, allowing designers and engineers to see how optical systems will perform without the need for prototyping. Speos software can be used from the early concept feasibility stage through the validation stages.

Speos software considers the colors, materials, and potential locations of a lighting system in the early design stages to visualize how the light might look, and how the vehicle might look under those lighting conditions, well before tooling. This enables designers and engineers to see the system in the car before making any big decisions. Once a decision has been made on where a light or optical system will go, Speos software can be used to optimize the design itself, considering the limited packaging space, and facilitate more accurate CAD designs based on different component configurations, from an optomechanical perspective.

Speos software can then be used during the later development cycles to validate the lighting system’s behavior, appearance, and harmonization with other interior lighting systems. 

At this stage, developments typically include a mature lighting system, which passes all electrical, mechanical, and optical requirements, and is evaluated along with a fully modeled car interior, along with environmental lighting conditions (day, dusk, night) — and all these scenarios can be brought into Speos software models to build an immersive validation environment.

There are various short- and long-term trends emerging that give a glimpse into what the future of automotive interior lighting might look like.

Safety Lights for Autonomous Cars

Ambient lighting that provides safety information to drivers is becoming more common, especially with the rise of autonomous and semi-autonomous vehicles.

With the increasing interest in autonomous vehicles, advanced displays are also being developed to inform drivers of any safety issues via coordinated light pulses — such as the lights blinking or pulsating in a certain color (red, for example) to alert a driver to grab the steering wheel if they’re about to hit a biker or are falling asleep.

Smart Glass

There is also a rise in smart glass and augmented reality displays, involving nano-micro scale photonics components emitting onto, or inside of, a windshield or other glass component. These can be found in heads-up displays, or elsewhere in the vehicle’s interior where information is not usually displayed — such as door panels or the sunroof glass.

A lot of concept vehicles are displaying information in non-traditional locations using smart glass, but many premium production vehicles are already using them today.

Sustainable Materials

Ultimately, lighting systems will become more efficient and sustainable through new or recycled materials that are better for the environment while ensuring that the light system still functions optimally.

Interior lighting in a car is less regulated than exterior lighting, so there are more material options available to designers to tailor the systems to each vehicle. 

However, with greater choice comes greater design difficulty, because there are more potential lighting option combinations that could theoretically be utilized. 

The design and validation process relies on simulation software such as Ansys Speos to determine the best materials and interior lighting kits to use throughout the design process. Speos software also helps balance style and functionality without the need for expensive prototyping.

Find out more about how Speos software can be used to solve your interior automotive lighting design challenges by contacting our technical team today.

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