Solar road studs are flashing solar cell powered LED maintenance-free lighting devices used in road construction to delineate road edges and centrelines. Embedded in the road surface, they are an electronic 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 900 m under favourable conditions.