ASTM F1252-21

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it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: F1252 − 16 F1252 − 21
Standard Test Method for
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Measuring Optical Reflectivity of Transparent Materials
This standard is issued under the fixed designation F1252; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This test method covers a procedure for measuring the reflectivity of transparent materials, hereafter known as specimens. The
results are repeatable without specifying a particular brand name of instrumentation.
1.2 This test method applies to substantially flat parts. Errors in measurement can occur if the parts being measured are not
substantially flat.
1.3 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this
standard.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Terminology
2.1 Definitions:
2.1.1 angle of incidence (Θ ), n—in the plane of the light source, specimen, and photometer, the angle of incidence is the angle
i
between the incident light ray and the normal to the surface (see Fig. 1).
2.1.2 angle of reflection (Θ ), n—in the plane of the light source, specimen, and photometer, the angle of reflection is the angle
r
between the reflected light ray and the normal to the surface (see Fig. 1).
2.1.3 light source, n—unless otherwise specified, the National Institute of Standards and Technology (NIST) diffused nonpolarized
Standard Illuminance A or C light source shall be used. The light source size shall be such that there shall be sufficient overlap
of the front and rear images on the specimen to overfill the measurement field size of the photometer. This measurement field size,
and front and back reflected image overlap, are illustrated in Fig. 2. (As angle of incidence and specimen thickness increase, the
two images will diverge.) The light source used shall be specified and reported as part of the test results.
2.1.4 measurement field size, n—the angular extent, in degrees or arc minutes, of the measurement aperture of the photometer.
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This test method is under the jurisdiction of ASTM Committee F07 on Aerospace and Aircraft and is the direct responsibility of Subcommittee F07.08 on Transparent
Enclosures and Materials.
Current edition approved April 1, 2016May 1, 2021. Published April 2016May 2021. Originally approved in 1989. Last previous edition approved in 20102016 as
F1252 – 10.F1252 – 16. DOI: 10.1520/F1252-16.10.1520/F1252-21.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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F1252 − 21
FIG. 1 Apparatus Set-Up
FIG. 2 Photometer Measurement Field Size (Aperture) Compared to Specimen Front and Back Surface Reflections
2.1.5 photometer, n—any commercial photometer or photopic filtered radiometer with a suitable measurement field size (1° or
smaller is recommended). A model with a viewfinder is recommended.
2.1.6 pivot point, n—the point in space at which the incident light ray and reflected light ray are to intersect (see Fig. 1).
2.1.7 reflectivity, adj—the reflectivity of a transparent specimen is defined as the ratio of the luminance of the reflected image of
a light source to the luminance of the light source. The reflectivity will depend upon several factors: the angle at which the reflected
light is measured, the thickness, surface quality, and type of material of the specimen, whether the specimen is coated, the spectral
distribution of the light source, and the spectral sensitivity of the measurement device. The reflectivity, as defined here, includes
the small amount of scattered light that contributes to the luminance of the reflected image.
3. Summary of Test Method
3.1 The luminance of the standard source is determined
...