Recommendations on the viewing distance of light field displays

Light field visualization is an emerging 3D technology that does not rely on viewing devices, such as special glasses. Without the need for such additional devices, multiple users may simultaneously enjoy the glasses-free 3D experience from a virtually infinite number of viewing positions, as the motion parallax is continuous and smooth. Although this immensely valuable property of light field displays does enable a great deal of viewing freedom, the proper perception of the visualized content still depends on the position of the observer. Position in this context determines the distance and the angle of the observer, with respect to the screen of the display. The validity of the latter is relatively straightforward to assess: if the observer is viewing the screen from inside the angle set by the field of view of the display, then the content shall be seen from its perceptually correct angle. However, the fundamental issue with the underinvestigated topic of viewing distance is that light field visualization may lose its 3D nature if viewed from a far-away position. This is due to the fact that in such a case, a single point of the screen may emit identical rays of light towards the two pupils of the observer. Therefore, the deficiency of disparity, the lack of distinct rays may lead to a 2D visual experience, nullifying the core scientific contribution of this technology. Of course, moving sideways in front of a horizontal-only-parallax display may, in fact, induce a 3D experience via the natural sense of parallax, but it should be applicable regardless of movement. Needless to say, in a multitude of professional environments, the users of such displays are not expected to be highly mobile during the work-related utilization of the technology. However, at the time of this paper, merely a few publications of the scientific literature address the topic of viewing distance, and standardization efforts are still in a rather early phase. Summa summarum, light field displays need clear guidelines with regard to viewing distance, which may benefit both the manufacturers and the users. Such guiding principles may make development and production more cost-efficient and user-oriented, and may contribute to the increased efficiency of usage-focused display design. In this paper, we provide a series of recommendations on the viewing distance of light field displays. The displays are separately analyzed within the context of their own use cases, taking into account the key performance indicators of both the apparatus and the visualized content, the various environmental conditions, as well as the relevant use-case-scenario-specific necessities and the professional requirements. The investigated use cases include medical imaging, telepresence, resource exploration, prototype review, training and education, gaming, digital signage, cinematography, cultural heritage exhibition, air traffic control and driver assistance systems.