Optical Measurements and Evaluations of Switchable Privacy Displays

Switchable Privacy Displays (SPD) enhance a wide range of applications, including codriver displays (CDD) in cars. SPDs can be switched between public and private modes. In public mode, a SP display is readable at all angles, unlike in private mode, where typically only a narrow angular range perpendicular to the display is readable. An important application is the CDD: Distracting content such as video is blocked for the driver, but visible for the codriver. We carried out many optical goniometric measurements of the characteristics of different SPD prototypes, such as luminance and color over viewing angle and uniformity. The latter was captured by a luminance imager and the horizontal line profiles were extracted to calculate the value of the Contrast Sensitivity Function (CSF) toward uniformity. An important parameter is the switching ratio SR, which describes the luminance ratio between driver and codriver. Evaluations with 20 subjects recommend a very low SR, resulting in a luminance of <0.1 cd/m² for the driver in private mode at night (the most critical case as there are no reflections of ambient light) to avoid distraction. Noticeable non-uniformity assessed for a CSF <5.