Limitations of today’s concepts
Presently, preparing LEDs for high light conformity requires substantial effort from manufacturers. This preparation process involves the measurement of the wavelength and brightness of the individual LEDs and then sorting them into categories – a process known as binning. This information is then included in the form of a barcode, a type of summary profile for each individual LED. The characteristics of each LED used are then stored in a system controller. From there, the data is transmitted to sub-controllers, to which groups of usually four RGB-LEDs are linked. Considering the large volumes of data that need to be transmitted in this manner, a fast SPI bus with a clock frequency of up to 50 MHz is normally used – resulting in further EMC-related challenges. It thus comes as no surprise that the substantial expenditures in terms of components, wiring, power supplies, EMC measures, etc. and the final calibration of the LED strip at the supplier dramatically raises the cost of such a "workaround".
This does not bode well for the vehicle manufacturers’ vision, which expects that up to 300 color (RGB) LEDs or more will be used per vehicle by 2021. There are further unpleasant restrictions: the data is received, read and then transmitted by each sub-controller according to the “shift register principle”. Consequently, the data transfer rate to the individual LEDs declines with the increasing number of LEDs mounted on the LED strip. This in effect makes attempting the implementation of sophisticated light effects in video speed for all practical intents and purposes quite unrealistic. Add to this the expectation that car interior lighting not only create a pleasant atmosphere (ambient light) but also perform functional tasks: for instance, to inform the driver of a self-driving car, whose eyes are not on the road or the display, that he/she must reassume control of the vehicle. Another functional task may be for the vehicle to signal to a pedestrian: “Yes – I have seen you and registered that you are about to cross the street.” This means that these LEDs will also have to meet stringent functional safety requirements whilst being diagnostic-capable – a feat well beyond the capabilities of today’s LED lighting systems.
The LED turns “digital”
The history dates back to the summer of 2002, where an extremely fruitful “brainstorming” session with BMW generated the "APIX" idea (Automotive Pixel Link), which has now surpassed 70 million installed automotive nodes and has become the undisputed and de-facto in-vehicle communications standard. In the summer of 2017, Inova launched the third-generation APIX3, enabling a bandwidth of 12 Gbit/s. The "digital LED" clearly carries many of the genes of APIX, especially its highly effective communications protocol.