ASTM F1252-08
(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 – 08
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 speci-
mens.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
FIG. 1 Apparatus Set-Up
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
2.1.4 measurement field size—the angular extent, in de-
priate safety and health practices and determine the applica-
grees, of the measurement aperture of the photometer.
bility of regulatory limitations prior to use.
2.1.5 photometer—any commercial photometer or photopic
filtered radiometer with a suitable measurement field size (1°
2. Terminology
or smaller is recommended). A model with a viewfinder is
2.1 Definitions:
recommended.
2.1.1 angle of incidence (Q)—in the plane of the light
i
2.1.6 pivot point—the point in space at which the incident
source, specimen, and photometer, the angle of incidence is the
light ray and reflected light ray are to intersect (see Fig. 1).
angle between the incident light ray and the normal to the
2.1.7 reflectivity—the reflectivity of a transparent specimen
surface (see Fig. 1).
is defined as the ratio of the luminance of the reflected image
2.1.2 angle of reflection (Q )—in the plane of the light
r
of a light source to the luminance of the light source. The
source, specimen, and photometer, the angle of reflection is the
reflectivitywilldependuponseveralfactors:theangleatwhich
angle between the reflected light ray and the normal to the
the reflected light is measured, the thickness, surface quality,
surface (see Fig. 1).
and type of material of the specimen, whether the specimen is
2.1.3 light source—unless otherwise specified, the National
coated, the spectral distribution of the light source, and the
Institute of Standards and Technology (NIST) diffused nonpo-
spectral sensitivity of the measurement device.The reflectivity,
larized Standard IlluminanceAor C light source shall be used.
as defined here, includes the small amount of scattered light
The light source size will be such that there will be sufficient
that contributes to the luminance of the reflected image.
overlap of the front and rear images on the specimen to overfill
the measurement field size of the photometer. This overlap is
3. Summary of Test Method
illustrated in Fig. 2. (As angle of incidence and specimen
3.1 The luminance of the standard source is determined by
thickness increase, the two images will diverge.) The light
measuring it directly with the photometer. The luminance of
source used should be specified and reported as part of the test
the reflection of the source is then measured off the specimen
results.
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 April 1, 2008. Published April 2008. Originally
approved in 1989. Last previous edition approved in 2002 as F1252 – 89(2002).
DOI: 10.1520/F1252-08. FIG. 2 Photometer Field of View
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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F1252 – 08
at a specified geometry. The luminance of the reflection is 5.5 A flat black surface (such as black velvet) may be
dividedbytheluminanceofthesourcetoobtainthereflectivity positioned behind (but not touching) the specimen during
of the specimen. measurement to reduce possible ambient light contamination
effects.
5.6 The photometer measurement aperture size (for ex-
4. Significance and Use
ample, 1°), the reference light source emitting surface size (for
4.1 Reflections from aircraft transparencies of instrument
example 5 cm circular), the distance from the reference light
lights and other cockpit objects have been a concern to many
source to the specimen, the distance from the photometer to the
pilots. Attempts to reduce these reflections ha
...
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:F1252–89(Reapproved2002) Designation: F 1252 – 08
Standard Test Method for
1
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 specimens.
The results are repeatable without specifying a particular brand name of instrumentation.
1.2The values stated in SI units are to be regarded as standard.
1.3
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 light ray 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 light ray to the surface (see Fig. 1).
2.1.3field of view (FOV)—the solid angle (degrees) that can be viewed through the photometer (see Fig. 2).
2.1.4
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 1°measurement field of view size of the photometer. This overlap is
illustrated in Fig. 32. (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. . (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 field of view of 1°. A model with a
viewfinder is recommended. —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
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 Oct. 27, 1989. Published December 1989.
Current edition approved April 1, 2008. Published April 2008. Originally approved in 1989. Last previous edition approved in 2002 as F 1252 – 89(2002).
Copyright © AS
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