# An Analysis of Visibility Requirements and Reaction Times of Near-Field Projections
## 1 Introduction
Therefore, in [PERSON]'s [13] analysis, a minimum Weber contrast of 0.4 is necessary to detect a projection while looking directly at the street. Compared to the second scenario, when looking at the phone while approaching the projection, the minimum contrast increased to 1. [PERSON] and [PERSON] discovered that the observer's reaction time decreases with the projections' higher luminance and contrast levels. Indeed, early detection of a near-field projection will reduce the risk for vulnerable RUs. Furthermore, [PERSON] and [PERSON] explain the higher severity of accidents during low-level ambient luminance, such as dusk and nighttime, with increasing reaction times. [22] In addition, [PERSON] [13] modified [PERSON]'s Relative Visual Performance Model [27] regarding reaction times with task-dependent factors for target size, luminance, and visibility level. The task-dependent factors play a significant role since the model is valid for simple detection tasks of squares or discs in a simplified laboratory environment, not a traffic environment [14; 27]. Moreover, the complexity of the projected illustration will have a significant impact, since both [PERSON] et al. [24] and [PERSON] et al. [25] discovered a relationship between the increasing complexity of Chinese characters and the coherent increase of visual acuity. According to [PERSON] et al. [25], Chinese CC1 characters are 37% less legible than English Sloan characters. In addition, [PERSON] et al. [24] discovered a similar tendency which indicates that Chinese characters require a higher visual acuity and a larger critical font size than English characters. After all, in metropolitan areas where many RUs interact, it is crucial to increase road safety with safety-relevant projections to reduce the risk of fatalities. Overall, the literature research shows that no studies have been carried out on the contrast perception near-field projections depending on the viewing distance, including reaction times. It is, therefore, important for future traffic in urban areas to understand whether the viewing distance and the resulting reaction time influence the perception of a subject and how this can be applied to the near-field projector's design. As [PERSON] and [PERSON] have already discovered, a higher brightness of the projection or a higher contrast should decrease the reaction time of the observer [22]. However, an arbitrary increase in the projector's illuminance will lead to energy-consuming vehicles in the future. Furthermore, the requirements for the visual performance will change dependent on the projection content if it is symbol- or text-based. Therefore, this study aims to validate the fundamental perception process for applying near-field projections. So, the subject study seeks to answer the question: 'Does content matter?' --and derive visibility requirements for near-field projections by analyzing the corresponding reaction times, the perceived Weber contrast by the participants for different content and to investigate the influence of the varying observation distances. Primarily, this subject study can guide the development of projection technology, the corresponding system efficiency, and the design of the projected content for vulnerable RUs to improve road safety. Thus, the following three research questions arise, which are to be answered using a psychophysical subject study:  
1. Does the projected content (symbol- or text-based) influence the photometric requirements, such as the detection contrast and the visibility level? 2. Does the projected content (symbol- or text-based) influence the participants' reaction times based on the detection probability? 3. Does the distance to the projection influence the photometric requirements, such as detection contrast or visibility level? Hence, the structure of this article is as follows: Section 2 depicts an overview of the study design with the materials and the procedure used to operate the subject study and methods to analyze the collected data.