The use of the film could draw greater attention to important traffic updates, benefitting both drivers and pedestrians, according to research recently published in the journal Science Advances.
The thin film is made up of polymer microspheres laid onto the sticky side of a transparent tape. The overall structure of the material leads to an interesting phenomenon when it is lit up by white light at night. Depending on the angle at which the observer is looking at the film and whether or not the light source is moving, some observers may see a single, stable colour reflected back, while others may see changing colours.
The material was developed at Fudan University in China, while additional research by optics experts at the University of Buffalo in New York helped develop potential uses for the material.
"You can use this material to make smart traffic signs," says Qiaoqiang Gan, an associate professor of electrical engineering in the University of Buffalo School of Engineering and Applied Sciences and a co-first author of the new study. "If a person is listening to loud music or isn't paying attention while they're walking or driving, a color-changing sign can help to better alert them to the traffic situation."
In one set of experiments, the film was used to create the characters on a speed limit sign, which the researchers then illuminated with a white light. When a fast-moving vehicle drove past, the colour of the film appeared to change from the driver’s perspective as the driver’s viewing angle changed.
In another experiment, the scientists applied the film to a series of markers at the side of the road, indicating the division of driving lanes. As a car approached the markers, the markers reflected the light from its headlights and lit up in bright colors. From inside the car, the colour of the markers remained the same, however for a stationary observer at the side of the road, the markers’ colour changed with the quickly moving light from the car’s headlights.
"If the car goes faster, the pedestrian will see the color change more quickly, so the sign tells you a lot about what is going on," says co-author Haomin Song, assistant professor of research in electrical engineering at the University at Buffalo.