Even though road signs already tend to be highly reflective, some night-time drivers still don't notice the things. New technology could help, as it causes signs to reflect in an attention-getting rainbow of changing colors.

Consisting of a thin transparent film covered on one side with polymer microspheres, the system is being developed by scientists at China's Fudan University, collaborating with optics experts from America's University at Buffalo. It works in either of two ways, which have already been successfully field-tested.

First of all, if a sign that's covered in the film is lit by a stationary white light, drivers speeding past it will still see it quickly changing between a variety of colors. This is because the perceived color changes with the angle at which the film is being viewed.

Secondly, if road-edge markers are covered in the film, stationary or slow-moving pedestrians will see them change color as they're illuminated by the headlights of passing cars. This is because the perceived color also changes with angle of the light that's hitting the film.

In both cases, the rate at which the colors change varies directly with the speed at which the car is travelling. Therefore, if drivers noticed that a road sign was changing colors quite rapidly, they would realize they were going too fast. Likewise, if a pedestrian saw that the road-edge markers were very quickly changing color, they'd know that a potentially-dangerous vehicle was approaching them from behind.

The effect all comes down to the microphotonic structure of the tiny spheres.

"Just like a prism can split a white light into a rainbow, this microsphere coating delivers another way to selectively reflect a part of the white light and result in a colorful image," U Buffalo's Assoc. Prof. Qiaoqiang Gan tells us. "In particular, this color reflection is heavily dependent on the incident angle and/or observation angle."

A paper on the research was recently published in the journal Science Advances.

And should you be interested in getting a color-changing jacket that works in a manner somewhat similar to that of the road sign film, check out the latest offering from Vollebak.