ASTM E810-20 Standard Test Method for Retroreflective Coefficient of Retroreflective Sheeting Using Coplanar Geometry

The standard “ASTM E810-20 Standard test method for retroreflective coefficient of retroreflective sheets using coplanar geometry” published by the American Society for Testing and Materials (ASTM) describes a test method that includes an instrument measurement of the retroreflective performance of retroreflective sheets.

The user of this test method must specify the entrance and observation angles and the rotation angles to be used. This test method is designed as a laboratory test and requires a facility that can be sufficiently darkened so that stray light does not affect the test results. The test apparatus must be capable of achieving coplanar geometry.

Portable and bench retroreflective measuring equipment may be used to determine the retroreflectance coefficient (RA) values ​​provided that the geometry measured in accordance with this test method and suitable substitute standard reference panels are used. In this case, the methods of Procedure B described in ASTM E809-21 Standard Practice for Measurement of Photometric Properties of Retroreflectors apply. Additional information on the use of portable retroreflectometers is included in ASTM E1709-09 Standard Test Method for Measurement of Retroreflective Signals Using a Portable Retroreflectometer with a 0,2-degree Observation Angle.

For the purposes of this standard, in addition to the terms and definitions given in “ASTM E284-22 Standard Terminology for Appearance” and “ASTM E808-01 Standard Practice for Describing Retroreflection,” the following definitions apply:

• The retroreflection coefficient (RA) is the ratio of the luminous intensity coefficient to the area of ​​a flat retroreflective surface. RA is a useful engineering quantity for determining the photometric performance of retroreflective surfaces such as highway delineators or warning devices. RA can also be used to determine the minimum retroreflective sheet area required for a desired level of photometric performance. RA has been widely used in the specification of retroreflective sheets.
• Coplanar geometry is the geometry of retroreflection in which the retroreflector axis, illumination axis and observation axis lie in the same plane. In coplanar geometry, the second angle of incidence is equal to 0 degrees, the presentation angle is equal to 0 degrees or 180 degrees, the orientation angle is equal to plus 180 degrees or minus 180 degrees.
• The reference axis refers to a half-line drawn from the retroreflector center perpendicular to the retroreflector axis.
• A reference mark is an indicator on a retroreflector that determines the orientation of the reference axis, outside the axis of the retroreflector.
• The entrance angle is the angle between the illumination axis and the retroreflector axis. The entrance angle is usually not greater than 90 degrees, but for completeness it is defined as the full range 0-180 degrees.
• A goniometer is an instrument used to measure or set angles.
• The illumination axis is the half-line from the retroreflector center to the source point.
• The angle of observation is the angle between the illumination axis and the observation axis. The angle of observation is never negative and is almost always less than 10 degrees and usually not more than 2 degrees. The full range is defined as 0-180 degrees.

This test method involves the use of a light projector source, a receiver, a device for positioning the receiver relative to the source, and a test specimen holder in a suitable dark area. The specimen holder is 15 m from the light source. The general procedure is to determine the ratio of light reflected from the test surface to light incident on the test surface. The photometric quantity, the retroreflection coefficient, is calculated from these measurements.

Measurements made with this test method relate to visual observations of retroreflective sheets as seen by the human eye when illuminated by tungsten filament light sources such as motor vehicle headlights.

The values ​​determined relate to the visual effects for a particular geometric configuration specified by the user of the test method. This test method has been found useful for testing at observation angles between 0,1 and 2,0 degrees (observation angles between 0,1 and 0,2 degrees can be achieved by careful design of the source and receiver aperture configuration) and at entrance angles up to 60 degrees.

The sampling procedure used for this test method shall be such that the test material is representative of the roll or lot. When testing a roll of retroreflective sheeting, a minimum of three 0,2 x 0,2 m samples shall be taken from the roll. These shall represent any cross-web and down-web variations. The average value of these three samples shall be reported.

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