Solar road studs are flashing solar-cell powered LED, maintenance-free lighting devices used in road construction. These help to  delineate road edges and centre lines. They are embedded in the road surface and are an improvement on the traditional cat's eyes in that they may give drivers more than a thirty-second reaction window (Compared with about 3 seconds for conventional reflective devices). The intense brightness of the LEDs makes them easily visible at distances of about 900m under favourable conditions.