ASTM F1252-89(1996)
(Test Method)Standard Test Method for Measuring Optical Reflectivity of Transparent Materials
Standard Test Method for Measuring Optical Reflectivity of Transparent Materials
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 The values stated in SI units are to be regarded as standard.
1.3 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 and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: F 1252 – 89 (Reapproved 1996)
Standard Test Method for
Measuring Optical Reflectivity of Transparent Materials
This standard is issued under the fixed designation F 1252; 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 (e) 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 speci-
mens. The results are repeatable without specifying a particular
brand name of instrumentation.
1.2 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 appro-
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
1.3 The preferred units are acceptable metric units.
FIG. 1 Apparatus Set-Up
2. Terminology
2.1 Definitions:
of a light source to the luminance of the light source. The
2.1.1 angle of incidence (Q )—in the plane of the light
i
reflectivity will depend upon several factors: the angle at which
source, specimen, and photometer, the angle of incidence is the
the reflected light is measured, the thickness, surface quality,
angle between the incident light ray and the normal light ray to
and type of material of the specimen, whether the specimen is
the surface (see Fig. 1).
coated, the spectral distribution of the light source, and the
2.1.2 angle of reflection (Q )—in the plane of the light
r
spectral sensitivity of the measurement device. The reflectivity,
source, specimen, and photometer, the angle of reflection is the
as defined here, includes the small amount of scattered light
angle between the reflected light ray and the normal light ray
that contributes to the luminance of the reflected image.
to the surface (see Fig. 1).
2.1.3 field of view (FOV)—the solid angle (degrees) that can
3. Summary of Test Method
be viewed through the photometer (see Fig. 2).
3.1 The luminance of the standard source is determined by
2.1.4 light source—unless otherwise specified, the National
Institute of Standards and Technology (NIST) diffused nonpo-
larized Standard Illuminance C light source shall be used. The
light source size will be such that there will be sufficient
overlap of the front and rear images on the specimen to overfill
the 1° field of view of the photometer. This overlap is
illustrated in Fig. 3. (As angle of incidence and specimen
thickness increase, the two images will diverge.) If a light
source other than the NIST Illuminant C is used, it should be
specified and reported as part of the test results.
2.1.5 photometer—any commercial photometer or photopic
filtered radiometer with a field of view of 1°. A model with a
viewfinder is recommended.
2.1.6 pivot point—the point in space at which the incident
FIG. 2 Image Overlap
light ray and reflected light ray are to intersect (see Fig. 1).
2.1.7 reflectivity—the reflectivity of a transparent specimen
is defined as the ratio of the luminance of the reflected image
This test method is under the jurisdiction of ASTM Committee F-7 on
Aerospace and Aircraft and is the direct responsibility of Subcommittee F07.08 on
Transparent Enclosures and Materials.
Current edition approved Oct. 27, 1989. Published December 1989. FIG. 3 Photometer Field of View
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
F 1252
measuring it directly with the photometer. The luminance of 6.2 The pivot point is the point in space at which the surface
the reflection of the source is then measured off the specimen of the specimen will be placed (6.5) such that the reflection
at a specified geometry. The luminance of the reflection is occurs at the desired geometry. Establish the pivot point by
divided by the luminance of the source to obtain the reflectivity marking the point with a small object, such as a piece of
of the specimen. cardboard. Position the light source at a proper distance from
the pivot point (5.3).
4. Significance and Use
6.3 Locate the photometer at a position equidistant from the
4.1 Reflections from aircraft transparencies of instrument
pivot point such that the source, pivot point, and photometer
lights and other cockpit objects have been a concern to many
are in line (see Fig. 4). Direct the photometer such that its FOV
pilots. Attempts to reduce these reflections have been ham-
pered by the lack of a repeatable measurement method and
variances in reflection measuring instrumentation. The prob-
lem with measuring instrumentation is that different brands
will often give significant value differences using the same
specimen surface.
4.2 This test method reduces the instrument variations by
standardizing the light source, calculation method, and area of
specimen surface being measured; a brand of instrumentation
is not specified. Since the reflectivity is defined as the ratio of
two luminance measurements and does not depend on an
absolute measurement, dependence upon the accuracy of the
measuring instrument is reduced.
FIG. 4 Apparatus Set-Up for Source Measurement
4.3 The test method may be used to objectively compare the
reflection characteristics of various transparent materials. Fur-
is centered on the luminance source. Focus the photometer on
thermore, the test method may be used to evaluate reflections
the source and record the luminance L.
of a specified spectral source by using that source in place of
6.4 Locate the photometer at a position equidistant from the
the standard light source.
pivot point such that the angle between the source, pivot point,
4.4 Provisions are made to check for polarization effects of
and photometer is twice the desired angle of incidence (see
the sample and to record the reflectivity of a standard speci-
Fig. 1). Direct the photometer such that the pivot point is
men. These provisions ar
...
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