Perceived Brightness vs. Required Sunlight Luminance of RGB Lighting on Automotive Dashboards

Colored light for visual communication with drivers and passengers at daylight conditions has recently started and increase in autonomous cars. The main use is safe visualization of the driving mode and warnings by a RGB LED pixelated light guide with at the bottom of the windshield. Today’s white luminance for daylight is 1,250 cd/m² with a RGB luminance ratio of typically 30:60:10. However, an OEM proposed recently this luminance just for blue, which is 10x the current luminance. Fundamentals of measurements and vision for blue are a low luminance due to V(lambda) but high color perception Color Matching Functions. The ratio of traffic signs (EN12966) is 35:50:15. Our car mock-up provides a white luminance of 13,000 cd/m² reaching 1,500 cd/m² for blue. The surrounding simulates night to sunlight with additional blinding. We tested 18 persons. The luminance of blue for “annoying” was 900 cd/m² for direct sunlight. Furthermore, the subjects had to adjust two neighboring colors to the same brightness or judge (brighter, same, darker) for different colors. The RGB luminance ratio as mean value is 28:56:16. A luminance of 500 cd/m² and blinking is a reasonable value for blue.