A retroreflectometer is an instrument used to objectively measure the retroreflectivity of surfaces and materials. Retroreflectometers can be used for field measurements as well as production measurements. The characteristics of this device are required to comply with regulations regarding reflective materials on highway traffic signs, high-visibility clothing, license plates, and reflective tape.
Retroreflection is the ability of some materials to reflect most of the light that falls on a surface in the same direction as the surface but in the opposite direction.
To measure retroreflection it is necessary to consider:
- Observation Angle (α), which measures the angular position of the eye relative to the center of the retroreflected beam.
- Illumination angle (β), ie the angle at which incident light enters the retroreflective surface.
Coefficient of retroreflection
The coefficient of retroreflection RA is the quotient between the brightness of an area of the signal in a given direction and the illuminance of that area. The unit of RA is (cd lx -1 m -2 ). RA is an important factor in the on-site quality control of traffic signs.
However, the value of RA depends on the viewing angle (α). Angle of view measures the angular position of the driver's eyes relative to the center of the retroreflected beam. When the viewing angle (α) increases, the value of RA decreases. For this purpose, the minimum value of RA was determined according to the values of the angle of incidence (β) and the angle of observation (α) of the incident light in the traffic sign.
