ASTM F1252-10
(Test Method)Standard Test Method for Measuring Optical Reflectivity of Transparent Materials
Standard Test Method for Measuring Optical Reflectivity of Transparent Materials
SIGNIFICANCE AND USE
Reflections from aircraft transparencies of instrument lights and other cockpit objects have been a concern to many pilots. Attempts to reduce these reflections have been hampered by the lack of a repeatable measurement method and variances in reflection measuring instrumentation. The problem with measuring instrumentation is that different brands will often give significant value differences using the same specimen surface.
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.
The test method may be used to objectively compare the reflection characteristics of various transparent materials. Furthermore, the test method may be used to evaluate reflections of a specified spectral source by using that source in place of the standard light source.
Provisions are made to check for polarization effects of the sample and to record the reflectivity of a standard specimen. These provisions are offered as an option to the tester; it is up to the user or the requiring agency to determine the significance and use of these data.
Since the reflections are measured photopically, the results are representative of what the pilot would visually perceive.
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 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 and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:F1252 −10
StandardTest Method for
1
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 thickness increase, the two images will diverge.) The light
source used should be specified and reported as part of the test
1.1 This test method covers a procedure for measuring the
results.
reflectivity of transparent materials, hereafter known as speci-
2.1.4 measurement field size—theangularextent,indegrees,
mens.The results are repeatable without specifying a particular
of the measurement aperture of the photometer.
brand name of instrumentation.
2.1.5 photometer—any commercial photometer or photopic
1.2 This test method applies to substantially flat parts.
filtered radiometer with a suitable measurement field size (1°
Errors in measurement can occur if the parts being measured
or smaller is recommended). A model with a viewfinder is
are not substantially flat.
recommended.
1.3 The values stated in SI units are to be regarded as
2.1.6 pivot point—the point in space at which the incident
standard. No other units of measurement are included in this
light ray and reflected light ray are to intersect (see Fig. 1).
standard.
2.1.7 reflectivity—the reflectivity of a transparent specimen
1.4 This standard does not purport to address all of the
is defined as the ratio of the luminance of the reflected image
safety concerns, if any, associated with its use. It is the
of a light source to the luminance of the light source. The
responsibility of the user of this standard to establish appro-
reflectivitywilldependuponseveralfactors:theangleatwhich
priate safety and health practices and determine the applica-
the reflected light is measured, the thickness, surface quality,
bility of regulatory limitations prior to use.
and type of material of the specimen, whether the specimen is
coated, the spectral distribution of the light source, and the
2. Terminology
spectral sensitivity of the measurement device.The reflectivity,
as defined here, includes the small amount of scattered light
2.1 Definitions:
that contributes to the luminance of the reflected image.
2.1.1 angle of incidence (Θ)—in the plane of the light
i
source, specimen, and photometer, the angle of incidence is the
3. Summary of Test Method
angle between the incident light ray and the normal to the
3.1 The luminance of the standard source is determined by
surface (see Fig. 1).
measuring it directly with the photometer. The luminance of
2.1.2 angle of reflection (Θ)—in the plane of the light
r
the reflection of the source is then measured off the specimen
source, specimen, and photometer, the angle of reflection is the
at a specified geometry. The luminance of the reflection is
angle between the reflected light ray and the normal to the
divided by the luminance of the source to obtain the reflectivity
surface (see Fig. 1).
of the specimen.
2.1.3 light source—unless otherwise specified, the National
4. Significance and Use
Institute of Standards and Technology (NIST) diffused nonpo-
larized Standard IlluminanceAor C light source shall be used. 4.1 Reflections from aircraft transparencies of instrument
The light source size will be such that there will be sufficient lights and other cockpit objects have been a concern to many
overlap of the front and rear images on the specimen to overfill pilots. Attempts to reduce these reflections have been ham-
pered by the lack of a repeatable measurement method and
the measurement field size of the photometer. This overlap is
illustrated in Fig. 2. (As angle of incidence and specimen 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.
1
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
4.2 This test method reduces the instrument variations by
Transparent Enclosures and Materials.
standardizing the light source, calculation method, and area of
Current edition approved Dec. 1, 2010. Published January 2011. Originally
specimen surface being measured; a brand of instrumentation
approved in 1989. Last previous edition approved in 2008 as F1252 – 08. DOI:
10.1520/F1252-10. is not specified. Since the reflectivity is defined as the ratio of
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
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:F1252–08 Designation: F1252 – 10
Standard Test Method for
1
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 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 and health practices and determine the applicability of regulatory
limitations prior to use.
2. Terminology
2.1 Definitions:
2.1.1 angle of incidence (Q) —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 (Q ) —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—unlessotherwisespecified,theNationalInstituteofStandardsandTechnology(NIST)diffusednonpolarized
Standard Illuminance A or 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 measurement field size of the photometer. This overlap is illustrated in
Fig. 2. (As angle of incidence and specimen thickness increase, the two images will diverge.) The light source used should be
specified and reported as part of the test results.
2.1.4 measurement field size—the angular extent, in degrees, of the measurement aperture of the photometer.
2.1.5 photometer—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—the point in space at which the incident 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 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 by measuring it directly with the photometer. The luminance of the
reflection of the source is then measured off the specimen at a specified geometry. The luminance of the reflection is divided by
the luminance of the source to obtain the reflectivity of the specimen.
4. Significance and Use
4.1 Reflections from aircraft transparencies of instrument lights and other cockpit objects have been a concern to many pilots.
Attempts to reduce these reflections have been hampered by the lack of a repeatable measurement method and variances in
reflection measuring instrumentation. The problem with measuring instrumentation is that different brands will often give
significant value differences using the same specimen surface.
1
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 AprilDec. 1, 2008.2010. Published April 2008.January 2011. Originally approved in 1989. Last previous edition approved in 20022008 as
F1252–89(2002).F1252 – 08. DOI: 10.1520/F1252-108.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700
...
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