Lanes on roads are traditionally marked in a passive way with reflecting road studs and high visibility paint, often coupled with other reflectors on short posts at the sides of the highway. However, on busy roads with dipped headlights these "passive road studs" are harder to see, and the range of visibility is dramatically reduced, while in wet conditions they can become completely invisible. Recently some new solar road stud markers have appeared as options for roadway designers, and a simple approach to the new trend is accounted here.
Solar road stud marker is an active road stud with automatic switching function, realized using the combination of a small solar panel, re-chargeable cell, and LED driver circuitry.
In addition to emitting light, an LED of solar road stud can be used as a light sensor to produce a current that is proportional to the intensity of the light. This capability can be used in a variety of applications including bidirectional optical communications. As a photodiode, an LED of solar road stud is sensitive to wavelengths equal to (or shorter than) the predominant wavelength it emits.
For instance, a green LED would be sensitive to blue light and to some green light, but not to yellow or red light. An LED with a clear plastic encapsulation (transparent type) will be more sensitive to broad-spectrum illumination than an LED with colored encapsulation (diffused type).
Roadway lighting systems such as solar road stud markers are now widely accepted as essential for controlling traffic flow in a wide number of applications. In practice, solar road studs operate well above the road surface and use a number of well known and widely accepted colours, solar road stud with LED lights in particular orientations to make the message to a driver clear and univocal thereby improving the outturn of the road while enhancing safety aspects.