Retroreflective Material for Nighttime Color-Changing Road Signs

A thin film that reflects light could be used to make road signs that shine brightly and change color at night. The film consists of polymer microspheres laid down on the sticky side of a transparent tape. The material’s physical structure leads to an interesting phenomenon: When white light shines on the film at night, some observers will see a single, stable color reflected back while others will see changing colors. The phenomenon depends on the angle of observation and whether the light source is moving.