Light in the vehicle not only has the function of making the occupants feel comfortable, but it also fulfills safety functions. With the ISELED, up to 4000 individual LEDs can be addressed.
Light in the vehicle not only has the function of making the occupants feel comfortable, but it also fulfills safety functions. With the ISELED, up to 4000 individual LEDs can be addressed.
( Bild: BMW)

LEds The advantages of networked LEDs in the vehicle

Author / Editor: Robert Isele and Franziska Hertlein * / Jochen Schwab

Light in the vehicle not only has an emotional aspect, but also serves safety. BMW is working on the ISELED, in which an LED and logic controller form a unit. BMW is already well advanced in the field of light as a supporting medium.

Anyone getting into a modern vehicle today will often notice a large display and lighting that is no longer limited to the cockpit. Interior lighting has undergone rapid development in recent years. Whereas ten years ago there were mainly filament lamps and occasionally networked monochrome LEDs in vehicles, the number of installed LEDs for interior lighting has steadily increased, as is the case with the BMW Group. For example, the BMW i3 from 2013 had only three discretely wired LEDs. In this application, the customer's perceptible change in the LED light was not solved due to the typical LED bandwidth of brightness and color from production and the changes during operation.

As the industrialization of LEDs progressed, the next LED generation came very quickly. For the BMW i8 from 2013 with ten LEDs in RGB, LIN-capable LEDs were developed for the first time. The LED binnings were optimized and a component-specific calibration was introduced to further develop the color stability under almost all conditions. In addition, the developers were able to solve the problem of discrete wiring. The current BMW X7 from 2018 shows how rapidly the trend towards the use of light for high-quality interior design has developed: There are already 44 RGB light points installed in the interior. However, a single LIN already reaches its technical limit with 26 LEDs, which is why two LINs per vehicle have already been installed within the vehicle architecture since the BMW 7 Series from 2016.

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Light in autonomous vehicles offers new possibilities

According to BMW, customer requirements for interior lighting have grown steadily in recent years. Similar to the growing market for lamps and luminaires for private users. For an automobile manufacturer, this means opening up new fields of innovation and further expanding existing ones. Here, new design approaches help to offer automotive customers varied light appearances in the form of decors, fluoroscopy or projections through clever design. The key here is a flexible color design and a variable lighting scenery in itself. Light should be an experience and at the same time enhance the driver's comfort.

The light communicates with the driver

Light can also communicate with the driver: Using parameters such as color, display location, and movement frequencies, the light can provide the driver with the necessary information or warn him in critical situations, thus increasing occupant safety. In order for the driver to be able to rely on the light display, it is of course essential that the light is displayed safely and clearly at all times. Autonomous driving will change the automotive industry: With the iNEXT vision, BMW has introduced a vehicle concept that can be a place of relaxation, interaction, entertainment or concentration. Accordingly, the interior resembles a modern, comfortable living room on four wheels. For the lighting design, for example: Productive lighting must be available for productive activities.

Light, therefore, has a supporting function. The work/reading area must be well lit so that possible shadows are avoided. It is therefore still best to position the light in the headliner, which must meet the usual requirements for color temperature design at different times of the day. The developers are working to ensure that the car automatically recognizes what the driver wants to do and what light is required to do this. If the driver unlocks the vehicle in a dark parking lot, the lights in the car already go on today. This enables the driver to find his car more quickly and when getting in it not only illuminates the puddles in front of the doors but also supports the boarding process by staging and then optimally illuminates all the storage areas in the interior. When the vehicle starts, the light is dimmed down to a comfortable level for the driving task.

The vehicle knows about the wishes of the occupants

At present, the driver often still operates manually via switches: the reading light is activated at the touch of a button. In the future, an autonomous vehicle will be able to recognize that the occupant is opening a book, where in the vehicle he is doing this and automatically switching on and aligning the reading light. The intelligence of the vehicle must therefore increase at this point for the comfort of the customer. The situation is similar in a smart home. Here, the networked building is equipped with sensors and control electronics to support the residents

To make this possible in automotive engineering, various technologies and control options are required in automobiles. With just one LED, it would be impossible to adequately illuminate different locations. These are the very requirements: more locations, but also mixes and different forms of light appearance. One application where these requirements come into play is the Follow-Me situation, in which the light cone must be able to follow a person. Light as a functional element and as a design element combined with attractive presentation will fundamentally change both the technology and the architecture of vehicle networking in the future.

LED and logic controller are one unit

At the launch of the current BMW X5 in November 2018, it became clear that high-speed networking of the LEDs would be necessary in the future. The next generation must be improved from the manufacturing process, easily scalable in number and application and cost-optimized, as well as easy to integrate into the vehicle. It quickly became clear: LED and logic controller would merge. ISELED was developed as a smart LED concept, with optimal networking and data rates of up to 2 MBit/s, in order to operate up to 4000 LEDs in milliseconds at almost video speed. The logic controller with integrated temperature compensation is optimized for power loss and is programmed directly with the calibration data for color and brightness during the LED manufacturing process. Problems with binnings and delivery dependencies of the classes are solved with MacAdams Step 1 accuracy and optimized yield for the product.

Display, light and sensors merge

In the onboard network, these smart LEDs are first connected via LIN hubs (ILH). Existing LIN LEDs are extended by multi-LED configurations. However, currently available RGB LEDs and multi-LED systems with LIN connection are only the necessary foundation for future customer functions. With the increasing dominance of display elements in vehicles, another technical trend is emerging: display/light and sensor technology are merging. This goes hand in hand with the next technical step: the networking of LIN LEDs, multi LEDs with LIN connection as well as sensors and other actuators in a field bus directly in the vehicle.

One possible step is the development of the ICN system. Such a network can connect switches, sensors, light and even simple projection systems via a central control software. LEDs that make optimum use of the defined infrastructure and enable additional features are therefore realistic. In terms of networking and smart functions, new applications are possible: for example matrix switching or LEDs with adjustable color temperature.

What to do with ISELED

The new technical possibilities created with ISELED provide the basis for further developments. The focus is always on the user when it comes to functional content. If the user is involved at an early stage, the design can be tailored entirely to his needs. Several years ago, the BMW Group began to consider in which situations supporting lighting effects could and should be displayed in the future. This original collection of use cases has now been divided into comprehensible categories with the help of user studies. Through interviews, the developers have gained valuable knowledge about how users want to be supported in different situations and which features of a lighting effect are decisive.

In order to combine the requirements with perceptual psychological principles, further studies were conducted. The focus was placed on the individual mode of action of the individual lighting components: How quickly can a driver react to different colors or types of movement of a lighting effect? Which distracts him from a primary activity? How beautiful is an effect perceived? And what influence does a customer's favorite color actually have? The comprehensive results allow conclusions to be drawn as to what a driver wants and what is most suitable in a particular situation with regard to the respective driving situation. The collected findings enable BMW to design attractive customer functions that offer the user an optimal, supportive experience across all driving situations.

This article was first published in German by Next Mobility.

* Robert Isele is Group Leader Night Design and Interior Light BMW Group Interior Electronics. Franziska Hertlein is a PhD student on the subject of user perception of dynamic interior light as a functional carrier..