As night falls, driving on the highway reveals many flashing lights ahead, along with clearly marked lane lines on the road surface. However, if you glance back, all you see is a dense, obscuring darkness, where even a single streetlight is absent. What causes this phenomenon?
On regular roads, streetlights are commonly installed. However, the illumination from these lights is quite low and can create light scattering, which often blinds drivers. This makes it difficult for them to recognize traffic signs, lane markings, and obstacles on the road. On highways, where traffic is heavy and speeds are high, adequate lighting is crucial. If street lighting impairs a driver’s visibility, it can lead to traffic accidents. Therefore, aside from gas stations, repair shops, and speed control points, highways typically do not use streetlights for illumination.
Despite this, driving on the highway remains very convenient. This is because a new type of sign, reflective devices, and retroreflective materials made from convex lenses are installed on roadside traffic signs and lane markings. Normally, these devices do not emit light; they only gather and reflect the strong beams from car headlights back towards the driver. The light 
reflected from these devices is hundreds of times stronger than regular paint, with a reflection distance of up to 1,000 meters. In other words, drivers can see these reflective points from over 1,000 meters away. Beyond 400 meters, they can distinguish colors, shapes, and symbols of the signs at around 200 meters and can even read the text on the signs. They shine like jewels along the highway, ensuring the safety and lives of travelers at night.
Convex retroreflectors are optical lenses with very high refractive indices used to attach to the metal frames of various objects. The diameter of these convex lenses is only half the thickness of a human hair. Typically, the reflection of objects on the road from headlights is diffuse and random; in other words, most of the light scatters in all directions, with only a small portion returning to the light source. Therefore, visibility is very low. The retroreflective film, after being irradiated by a metallic layer, directs the parallel light rays back toward the light source, allowing the illuminated surfaces of the objects to be clearly visible. As a result, retroreflective materials can shine brightly in the dark without consuming energy themselves.
Currently, these new types of reflective devices are not only used on highways but are also incorporated into the uniforms of traffic police and environmental workers… They will have a significant impact.
Hoang Hoa
