Retroreflection is the ability of certain materials to reflect most of the light that falls on a surface in the same direction as the surface but in the opposite direction.
For, measuring retroreflection needs to consider:
- Observation angle (α), measuring the angular position of the eye relative to the center of the retroreflected beam.
- Illumination angle (β), i.e. the angle at which the incident light enters the surface of the reflector.
To objectively measure the retroreflection of surfaces and materials, a device called a retroreflectometer is required. This type of instrument can be used both for field measurements and for measurements in production. In addition, retroreflectors need to comply with regulations regarding reflective materials on traffic signs, high-visibility clothing, license plates and reflective tape.
retroreflective material
Elements or surfaces that reflect light back to the source, regardless of the angle of incidence, are called retroreflectors.
In vertical traffic signs, vertical signage or high-visibility apparel, a small layer of microprisms or glass microspheres is often applied to make these elements retroreflective.
In the case of microprisms, when placed perpendicular to each other, the light beam is reflected back by a combination of three mirrors forming an angle.
However, in the case of glass microspheres, due to the arrangement of the reflective and refractive optical elements that make up the retroreflector, the focal surface of the refractive element coincides with the reflective surface.
Testing of Fixed Vertical Traffic Signs
The material properties of the surface of fixed vertical road markings are prescribed by regulations. Thus, the specification UNE-EN 12899 specifies the value of the minimum retroreflection coefficient in fixed signals.
The standard also stipulates the value of the retroreflection coefficient RA for the viewing angle and certain incident angles after the aging test is carried out.
On the other hand, ASTM E 1709 establishes a method for measuring the retroreflective properties of marking materials using a portable retroreflectometer at an observation angle of 0.2 degrees. A similar method for a 0.5 degree observation angle is established in standard ASTM E 2540.
High Visibility Clothing Testing
High-visibility clothing needs to have conspicuous properties, that is, it can immediately attract visual attention.
To determine this capacity, several factors need to be considered, such as brightness and color contrast. Other factors include design, configuration, and feature motion relative to the background environment that needs to be seen. The conspicuous property is especially important in complex environments where there are visual competitors.
UNE-EN ISO 20471 specifies minimum values for the coefficient of retroreflection. Specify these values for new materials and materials submitted to testing. Some of these tests are abrasion, bending, low temperature folding, temperature changes, the effects of rain, washing and dry cleaning.
On the other hand, the standard UNE-EN ISO 17353:2020 specifies the reflective performance requirements of new materials in protective clothing, especially for enhanced visibility equipment in medium risk situations. In addition, the standard specifies the method for carrying out the measurements. Protective clothing covered by this standard is equipment designed to provide visibility to users in moderate risk situations in any daylight condition and/or in low light conditions from vehicle headlights or reflectors in the dark.
road sign test
In addition to the above regulations, there are regulations applicable to retroreflective testing of other types of road markings.
This is the case with Part 3 of the UNE-EN 12899 standard, which focuses on new retroreflective profilers and devices for use in traffic flow areas. This part of the standard determines, inter alia, the color coordinates and luminance coefficients of eyeliner pens and reflector devices under daytime conditions. Likewise, it establishes the color coordinates of the retroreflective device under nighttime conditions. It also specifies the retroreflection coefficient of the retroreflective device.
On the other hand, the standard UNE-EN 13422:2020 deals with portable deformable warning devices and descriptors. That is, it is responsible for portable traffic signals on highways, like cones and cylinders.
In addition, the UNE 135902:2020 standard specifies the characteristics and test methods of urban road equipment, especially for retroreflective lane separator equipment.
UNE 135363: 1998 specifies the characteristics, measurements and test methods of beacons, in particular, cylindrical beacons in polymeric materials.
