1、Designation: F1252 10F1252 16Standard Test Method forMeasuring Optical Reflectivity of Transparent Materials1This standard is issued under the fixed designation F1252; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of las
2、t revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers a procedure for measuring the reflectivity of transparent materials, hereafter known as specimens
3、.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 notsubstantially flat.1.3 The values stated in SI units are to be regarded as standard.
4、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 responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicabi
5、lity of regulatorylimitations prior to use.2. Terminology2.1 Definitions:2.1.1 angle of incidence (i), nin the plane of the light source, specimen, and photometer, the angle of incidence is theangle between the incident light ray and the normal to the surface (see Fig. 1).2.1.2 angle of reflection (
6、r), nin the plane of the light source, specimen, and photometer, the angle of reflection is theangle between the reflected light ray and the normal to the surface (see Fig. 1).2.1.3 light sourcesource, nunless otherwise specified, the National Institute of Standards and Technology (NIST) diffusednon
7、polarized Standard Illuminance A or C light source shall be used. The light source size willshall be such that there willshallbe sufficient overlap of the front and rear images on the specimen to overfill the measurement field size of the photometer. Thisoverlap is measurement field size, and front
8、and back reflected image overlap, are illustrated in Fig. 2. (As angle of incidence andspecimen thickness increase, the two images will diverge.) The light source used shouldshall be specified and reported as part ofthe test results.2.1.4 measurement field sizesize, nthe angular extent, in degrees,
9、degrees or arc minutes, of the measurement aperture ofthe photometer.2.1.5 photometerphotometer, nany commercial photometer or photopic filtered radiometer with a suitable measurementfield size (1 or smaller is recommended). A model with a viewfinder is recommended.2.1.6 pivot pointpoint, nthe point
10、 in space at which the incident light ray and reflected light ray are to intersect (see Fig.1).2.1.7 reflectivityreflectivity, adjthe reflectivity of a transparent specimen is defined as the ratio of the luminance of thereflected image of a light source to the luminance of the light source. The refl
11、ectivity will depend upon several factors: the angleat which the reflected light is measured, the thickness, surface quality, and type of material of the specimen, whether the specimenis coated, the spectral distribution of the light source, and the spectral sensitivity of the measurement device. Th
12、e reflectivity, asdefined here, includes the small amount of scattered light that contributes to the luminance of the reflected image.3. Summary of Test Method3.1 The luminance of the standard source is determined by measuring it directly with the photometer. The luminance of thereflection of the so
13、urce source, from both the front and back surfaces of the specimen, is then measured off the specimen at aspecified geometry. The luminance of the reflection is divided by the luminance of the source to obtain the reflectivity of thespecimen.1 This test method is under the jurisdiction of ASTM Commi
14、ttee F07 on Aerospace and Aircraft and is the direct responsibility of Subcommittee F07.08 on TransparentEnclosures and Materials.Current edition approved Dec. 1, 2010April 1, 2016. Published January 2011April 2016. Originally approved in 1989. Last previous edition approved in 20082010 asF1252 08.F
15、1252 10. DOI: 10.1520/F1252-10.10.1520/F1252-16.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. Becauseit may not be technically possible to adequately depict all changes accurate
16、ly, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1
17、4. Significance and Use4.1 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 inreflection measuring instrument
18、ation. The problem with measuring instrumentation is that different brands will often givesignificant 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 ofspecimen surface being meas
19、ured; a brand of instrumentation is not specified. Since the reflectivity is defined as the ratio of twoluminance measurements and does not depend on an absolute measurement, dependence upon the accuracy of the calibration ofthe measuring instrument is reduced.4.3 The test method may be used to obje
20、ctively compare the reflection characteristics of various transparent materials.Furthermore, the test method may be used to evaluate reflections of a specified spectral source distribution light source (forexample, a monochromatic light-emitting diode) by using that source in place of the standard l
21、ight source.4.4 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 significanceand use of these data.4.5 Since
22、 the reflections are measured photopically, the results are representative of what the pilot would visually perceive.5. Apparatus and Setup5.1 The apparatus shall be set up as shown in Fig. 1.5.2 The angle of incidence i shall be determined by the user or requiring agency. Since i = r, the total ang
23、le of reflection = 2i = 2= 2r. i and r shall be accurate to within 60.5, hence shall be accurate to within 61.5.3 The distance from the light source to the specimen and from the specimen to the photometer is not critical. However, it isdesirable to position the light source relatively far from the s
24、ample (for example, 50 cm or more) to minimize the effects ofscattered light from the specimen contaminating the reflectivity measurement. The light source to specimen distance must be suchthat the reflected image viewed through the photometer is sufficiently large to overfill the photometer measure
25、ment field (see 2.1.3and Fig. 2). The distance from the specimen to the photometer must be short enough to ensure the reflected images overfill themeasurement aperture but long enough to ensure the photometer can focus on the image.FIG. 1 Apparatus Set-UpFIG. 2 Photometer Field of ViewMeasurement Fi
26、eld Size (Aperture) Compared to Specimen Front and Back Surface ReflectionsF1252 1625.4 The testing shall be done in a room with controlled lighting such that the photometer reading with the reference light offis less than 0.1 % of the reflection reading measured with the reference light on. This wi
27、ll ensure ambient room light contaminationof the results is less than 0.1 %.5.5 A flat black surface (such as black velvet) may be positioned behind (but not touching) the specimen during measurementto reduce possible ambient light contamination effects.5.6 The photometer measurement aperture size (
28、for example, 1), the reference light source emitting surface size (for example5 cm circular), the distance from the reference light source to the specimen, the distance from the photometer to the specimen andthe angle of incidence shouldshall all be included in the report.6. Procedure6.1 Allow the l
29、ight source and photometer to warm up per in accordance with the manufacturers specification.6.2 The pivot point is the point in space at which the front surface of the specimen willshall be placed (6.5) such that thereflection occurs at the desired geometry. Establish the pivot point by marking the
30、 point with a small object, such as a piece ofcardboard. Position the light source at a proper distance from the pivot point (5.3).6.3 Locate the photometer such that the light source, pivot point, and photometer are in line (see Fig. 3). Direct the photometersuch that its measurement field is cente
31、red on the light source. Focus the photometer on the light source and record the luminanceL.6.4 Locate the photometer at a position equidistant from the pivot point such that the angle between the source, pivot point, andphotometer is twice the desired angle of incidence2 (see Fig. 1). Direct the ph
32、otometer such that the pivot point is centered in theFOV.6.5 Position the specimen such that the center of the front surface is at the pivot point. Remove any object that may have beenused to mark the pivot point. Keeping the photometer and source fixed, adjust the attitude of the specimen until the
33、 image of thesource completely covers the photometers measurement field. Depending on the specimen, the image of the source may beseparated into two images due to reflections from the front and back surfaces of the specimen. specimen (Fig. 2). In this case,position the source such that the overlappi
34、ng region of the images is centered over the measurement field. Focus the photometeron the image of the source and measure the luminance of the source reflection using the specimen. Record this value as Ls.6.6 (Optional) Repeat the measurement as in 6.5 and with the transparent specimen rotated 90 a
35、round an axis normal to thesurface. Record this reading as Lp (see Fig. 4).6.7 Steps 6.3 6.6 shouldshall be repeated a minimum of three times for each specimen (varying the location of the reflectionupon the surface of the specimen each time) to account for localized variances in reflectivity and to
36、 establish repeatability.6.8 As an option to the user or requiring agency, a standard specimen may be identified. If so, perform steps 6.3 6.6 usingthe standard specimen. Record the luminance value as Lst.6.9 Fill out Fig. 5 to calculate the reflection.2 There exists a maximum angle of incidence for
37、 which measurements can be made. For the apparatus specified, this angle, max, depends only upon the size, thickness,size and index of refraction of the specimen. thickness of the specimen, and the size of the light source. A thin specimen four inches wide will permit measurements for up to 132. max
38、 will decrease as the specimen thickness increases. For most measurements a four inch wide specimen will be adequate; a larger width may be required forvery thick specimens and/or large values of .FIG. 3 Apparatus Set-Up for Source MeasurementF1252 1637. Precision and Bias37.1 PrecisionThis precisio
39、n section is based on a simulated interlaboratory study that was accomplished at a single laboratory.Repeatability was achieved by having a single operator make repeated measurements with a single photometer without changingthe measurement set-up. Reproducibility between laboratories was achievedsim
40、ulated by having the same operator completelydisassemble the measurement configuration and make another set of measurements after reassembling the measurementconfiguration at least two hours later. While not ideal, it is expected that this procedure should capture most of the varianceexpected from b
41、etween laboratory measurements. This is possible because the measurement procedure itself involves the ratio oftwo measurements made with the same light measuring instrument; therefore, even if the instrument is horribly miscalibrated, thefact that the calculated value is the ratio of two measuremen
42、ts eliminates calibration errors as a source of variance. Nevertheless,the following precision values should be considered optimistic (perhaps somewhat low) but they are more realistic than thepreviously published values and should serve until a proper, multi-laboratory, ILS is achieved.7.1.1 Table
43、1 summarizes the results of an Internal Laboratory Study conducted using Test Method F1252 08. To beconservative, the repeatability and reproducibility values in the following sections are based on the largest (worst) percent values(Columns 5 and 7) found in Table 1.7.1.2 RepeatabilityThe difference
44、 between successive results obtained by the same operator with the same apparatus underconstant operating conditions, would, in the long run, in the normal and correct operation of the test method exceed the followingvalues only in one case in twenty:The difference between successive results obtaine
45、d by the same operator with the same apparatus under constant operatingconditions, would, in the long run, in the normal and correct operation of the test method exceed the following values only in onecase in twenty:Repeatability = 0.15 % of coefficient valuevalue.3 Supporting data have been filed a
46、t ASTM International Headquarters and may be obtained by requesting Research Report RR:F07-1009.Reflection data Reflection CalculationsLuminance ofSource (L)Luminance ofReflection offSpecimen (Ls)Reflection ofRotatedSpecimen (Lp)(Optional)Reflection ofStandard(Optional)SpecimenReflectioncoefficient(
47、Ls/L)PolarizationCheck (Lp/K)(Optional)Glass Standard(Lst/L) (Optional)Run 1Run 2Run 3Sample Identification _ Date _Source Identification _ User _Standard Identification _FIG. 5 Calculation of ReflectionFIG. 4 Rotation of Sample for Polarization CheckTABLE 1 Summary of Internal Laboratory Study Resu
48、ltsSample Angle Degree Avg ReflectCoefficientRepeatabilityReflect. Coeff% ReproducibilityReflect Coeff%3 20 0.07537 0.00007 0.09 0.00042 0.553 30 0.07750 0.00011 0.15 0.00059 0.771 20 0.08196 0.00006 0.08 0.00058 0.711 30 0.08409 0.00005 0.06 0.00045 0.532B 20 0.33183 0.00015 0.04 0.00328 0.992B 30
49、0.33391 0.00046 0.14 0.00402 1.202A 20 0.34585 0.00037 0.11 0.00272 0.792A 30 0.34839 0.00025 0.07 0.00316 0.91F1252 164For example, if a measurement of a sample results in a reflection coefficient value of 0.08000, then only one time in twenty shoulda repeat measurement be different by more than 0.15 % of this value (0.08000) or by more than 0.00012. Similarly, if the samplewas measured to have a reflection coefficient of 0.50000,
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