Optical Performance of Exterior Displays

Autonomous cars should communicate with other road users, such as visualizing their driving mode or recognizing a pedestrian and the car will stop. Such displays must be sunlight readable and smoothly integrated into the front and rear of a car. We prototyped a full-scale mock-up to evaluate LCDs, LEDs and e-paper regarding optical performance. RGB LED matrix, monochrome and color reflective e-paper displays were optically evaluated by ambient light set-ups incl. a sampling sphere (SCI, SCE). The color e-paper showed a small color gamut which is about 10% of newspaper printing. This display was as well-rated as being poor in color performance by subjects. LED matrix displays are most suitable and can be integrated into the radiator grille and/or use the hidden display effect. Finally, we chose an 80 cm x 40 cm RGB LED display with 128 x 64 (h x v) pixel and 6 mm pixel pitch. However, LEDs with 3 mm and 6 mm were evaluated better than 12 mm at small distances, which are not typical for exterior displays. We conducted a survey with subjects regarding content (signs, text, icons ... for various use cases). RGB colored animated icons rate best; text should be rarely used.