## 2 Definition and Sorting  
As illustrated in Figure 1, in-vehicle lighting achieved by industrial realization major complexity and variability. A general definition and classification are performed based on this development in the following sections. According to a definition proposal a general ambient light system not only applies to the vehicle context: \"An ALS (ambient light system) is a system positioned in the periphery of a person's attention that conveys information using light encodings in a non-distracting way most of the time\" [6]. In addition, \"we consider ambient light systems as a subgroup of ambient displays that have a specific focus on a light modality as carrier of information in the periphery\" [6]. This definition might be suitable for some aspects, but cannot cover the complete spectrum specified of in-vehicle lighting. Therefore, we started to categorize previous research about in-vehicle lighting in three parts:  
* The first part focuses on technology driven approaches like new LED communication protocols, calibration processes for the single red-green-blue chips and temperature compensation methods including end of line testing and light-technical analysis [7, 8]. * The second part focuses on visual aspects which are directly motivated out of the presence of in-vehicle lighting systems. Examples for that are space perception, interior quality and functionality which are higher perceived with the attendance of these systems compared to those without [9]. These are used as a driving assistant like for a lane changing assistant [10, 11], brake accelerator [12] and parking assistant [13] or as a overtaking request indicator between manual and autonomous driving [14], and were designed with different visual stimuli but were not able to increase significantly the reaction time compared with no visual stimuli [15]. Compared to a display system, a LED light bar as a HMI warning interface achieved a higher subjective driver satisfaction rate but with missing significance [16]. In addition, trust in the vehicle [17] and steering reaction time are significantly improved with a supported in-vehicle lighting system for assistance compared to those without [18]. It is questionable if auditory or visual stimuli are more preferred for an autonomous driving vehicle-driver communication [19]. A combination of both might be suitable since a visual-accuracy and an auditory-reaction time relation was reported [20]. All these stimuli were placed in a peripheral vision area. For foveal vision, there might be an influence on the driver's road or traffic participant perception based on color and brightness changes by in-vehicle lighting [21]. Brightness studies for in-vehicle lighting within the coming visual communication approach are initialized also under daylight conditions [22]. Figure 1: Chronology of in-vehicle lighting system [3, 4, 5]. * The third part can be classically categorized to non-visual aspects. In a recent study, color, brightness and dynamic factors were varied and three car occupants' mood ratings about satisfaction, tension and unique were analyzed. They found a significant correlation between arousal with light color and dynamic [23]. Also, in-vehicle lighting can achieve a general positive effect on car occupants by increasing the concentration level on high-speed driving. In addition, an idea is also to reduce cognitive workload by in-vehicle lighting, which is currently only a concept [24]. On the other side, further study participants recognized the additional visual stimuli as distracting or causing higher stress level [25]. Furthermore, blue-enriched white in-vehicle light might have the potential as a counter measurement for driving fatigue by increasing reaction time, although precise driving tasks had less accuracy within this condition [26]. For a long wavelength orange light illumination, simulated driving behavior is constant but characterized with larger driving errors under blue light illumination with reduced reaction time [27].