1、Designation: F1252 10Standard 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 last revisi
2、on. 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 thereflectivity of transparent materials, hereafter known as speci-mens. The re
3、sults are repeatable without specifying a particularbrand name of instrumentation.1.2 This test method applies to substantially flat parts.Errors in measurement can occur if the parts being measuredare not substantially flat.1.3 The values stated in SI units are to be regarded asstandard. No other u
4、nits of measurement are included in thisstandard.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of re
5、gulatory limitations prior to use.2. Terminology2.1 Definitions:2.1.1 angle of incidence (Qi)in the plane of the lightsource, specimen, and photometer, the angle of incidence is theangle between the incident light ray and the normal to thesurface (see Fig. 1).2.1.2 angle of reflection (Qr)in the pla
6、ne of the lightsource, specimen, and photometer, the angle of reflection is theangle between the reflected light ray and the normal to thesurface (see Fig. 1).2.1.3 light sourceunless otherwise specified, the NationalInstitute of Standards and Technology (NIST) diffused nonpo-larized Standard Illumi
7、nance A or C light source shall be used.The light source size will be such that there will be sufficientoverlap of the front and rear images on the specimen to overfillthe measurement field size of the photometer. This overlap isillustrated in Fig. 2. (As angle of incidence and specimenthickness inc
8、rease, the two images will diverge.) The lightsource used should be specified and reported as part of the testresults.2.1.4 measurement field sizethe angular extent, in de-grees, of the measurement aperture of the photometer.2.1.5 photometerany commercial photometer or photopicfiltered radiometer wi
9、th a suitable measurement field size (1or smaller is recommended). A model with a viewfinder isrecommended.2.1.6 pivot pointthe point in space at which the incidentlight ray and reflected light ray are to intersect (see Fig. 1).2.1.7 reflectivitythe reflectivity of a transparent specimenis defined a
10、s the ratio of the luminance of the reflected imageof a light source to the luminance of the light source. Thereflectivity will depend upon several factors: the angle at whichthe reflected light is measured, the thickness, surface quality,and type of material of the specimen, whether the specimen is
11、coated, the spectral distribution of the light source, and thespectral sensitivity of the measurement device. The reflectivity,as defined here, includes the small amount of scattered lightthat contributes to the luminance of the reflected image.3. Summary of Test Method3.1 The luminance of the stand
12、ard source is determined bymeasuring it directly with the photometer. The luminance ofthe reflection of the source is then measured off the specimen1This test method is under the jurisdiction of ASTM Committee F07 onAerospace and Aircraft and is the direct responsibility of Subcommittee F07.08 onTra
13、nsparent Enclosures and Materials.Current edition approved Dec. 1, 2010. Published January 2011. Originallyapproved in 1989. Last previous edition approved in 2008 as F1252 08. DOI:10.1520/F1252-10.FIG. 1 Apparatus Set-UpFIG. 2 Photometer Field of View1Copyright ASTM International, 100 Barr Harbor D
14、rive, PO Box C700, West Conshohocken, PA 19428-2959, United States.at a specified geometry. The luminance of the reflection isdivided by the luminance of the source to obtain the reflectivityof the specimen.4. Significance and Use4.1 Reflections from aircraft transparencies of instrumentlights and o
15、ther cockpit objects have been a concern to manypilots. Attempts to reduce these reflections have been ham-pered by the lack of a repeatable measurement method andvariances in reflection measuring instrumentation. The prob-lem with measuring instrumentation is that different brandswill often give si
16、gnificant value differences using the samespecimen surface.4.2 This test method reduces the instrument variations bystandardizing the light source, calculation method, and area ofspecimen surface being measured; a brand of instrumentationis not specified. Since the reflectivity is defined as the rat
17、io oftwo luminance measurements and does not depend on anabsolute measurement, dependence upon the accuracy of themeasuring instrument is reduced.4.3 The test method may be used to objectively compare thereflection characteristics of various transparent materials. Fur-thermore, the test method may b
18、e used to evaluate reflectionsof a specified spectral source by using that source in place ofthe standard light source.4.4 Provisions are made to check for polarization effects ofthe sample and to record the reflectivity of a standard speci-men. These provisions are offered as an option to the teste
19、r; itis up to the user or the requiring agency to determine thesignificance and use of these data.4.5 Since the reflections are measured photopically, theresults are representative of what the pilot would visuallyperceive.5. Apparatus and Setup5.1 The apparatus shall be set up as shown in Fig. 1.5.2
20、 The angle of incidence Qishall be determined by theuser or requiring agency. Since Qi= Qr, the total angle ofreflection Q =2Qi=2Qr. Qiand Qrshall be accurate to within60.5, hence Q shall be accurate to within 61.5.3 The distance from the light source to the specimen andfrom the specimen to the phot
21、ometer is not critical. However,it is desirable to position the light source relatively far from thesample (for example, 50 cm or more) to minimize the effects ofscattered light from the specimen contaminating the reflectivitymeasurement. The light source to specimen distance must besuch that the re
22、flected image viewed through the photometer issufficiently large to overfill the photometer measurement field(see 2.1.3). The distance from the specimen to the photometermust be short enough to ensure the reflected images overfill themeasurement aperture but long enough to ensure the photom-eter can
23、 focus on the image.5.4 The testing shall be done in a room with controlledlighting such that the photometer reading with the referencelight off is less than 0.1 % of the reflection reading measuredwith the reference light on. This will ensure ambient room lightcontamination of the results is less t
24、han 0.1 %.5.5 A flat black surface (such as black velvet) may bepositioned behind (but not touching) the specimen duringmeasurement to reduce possible ambient light contaminationeffects.5.6 The photometer measurement aperture size (for ex-ample, 1), the reference light source emitting surface size (
25、forexample 5 cm circular), the distance from the reference lightsource to the specimen, the distance from the photometer to thespecimen and the angle of incidence should all be included inthe report.6. Procedure6.1 Allow the light source and photometer to warm up permanufacturers specification.6.2 T
26、he pivot point is the point in space at which the surfaceof the specimen will be placed (6.5) such that the reflectionoccurs at the desired geometry. Establish the pivot point bymarking the point with a small object, such as a piece ofcardboard. Position the light source at a proper distance fromthe
27、 pivot point (5.3).6.3 Locate the photometer such that the light source, pivotpoint, and photometer are in line (see Fig. 3). Direct thephotometer such that its measurement field is centered on thelight source. Focus the photometer on the light source andrecord the luminance L.6.4 Locate the photome
28、ter at a position equidistant from thepivot point such that the angle between the source, pivot point,and photometer is twice the desired angle of incidence2(seeFig. 1). Direct the photometer such that the pivot point iscentered in the FOV.6.5 Position the specimen such that the center of the fronts
29、urface is at the pivot point. Remove any object that may havebeen used to mark the pivot point. Keeping the photometer andsource fixed, adjust the attitude of the specimen until the imageof the source completely covers the photometers measurementfield. Depending on the specimen, the image of the sou
30、rce may2There exists a maximum angle of incidence for which measurements can bemade. For the apparatus specified, this angle, Qmax, depends only upon the size,thickness, and index of refraction of the specimen.Athin specimen four inches widewill permit measurements for Q up to 132. Qmaxwill decrease
31、 as the specimenthickness increases. For most measurements a four inch wide specimen will beadequate; a larger width may be required for very thick specimens and/or largevalues of Q.FIG. 3 Apparatus Set-Up for Source MeasurementF1252 102be separated into two images due to reflections from the fronta
32、nd back surfaces of the specimen. In this case, position thesource such that the overlapping region of the images iscentered over the measurement field. Focus the photometer onthe image of the source and measure the luminance of thesource reflection using the specimen. Record this value as Ls.6.6 (O
33、ptional) Repeat the measurement as in 6.5 and withthe transparent specimen rotated 90 around an axis normal tothe surface. Record this reading as Lp(see Fig. 4).6.7 Steps 6.3-6.6 should be repeated a minimum of threetimes for each specimen (varying the location of the reflectionupon the surface of t
34、he specimen each time) to account forlocalized variances in reflectivity and to establish repeatability.6.8 As an option to the user or requiring agency, a standardspecimen 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.
35、 5 to calculate the reflection.7. Precision and Bias37.1 PrecisionThis precision section is based on a simu-lated interlaboratory study that was accomplished at a singlelaboratory. Repeatability was achieved by having a singleoperator make repeated measurements with a single photom-eter without chan
36、ging the measurement set-up. Reproducibilitybetween laboratories was achieved by having the same opera-tor completely disassemble the measurement configuration andmake another set of measurements after reassembling themeasurement configuration at least two hours later. While notideal, it is expected
37、 that this procedure should capture most ofthe variance expected from between laboratory measurements.This is possible because the measurement procedure itselfinvolves the ratio of two measurements made with the samelight measuring instrument; therefore, even if the instrument ishorribly miscalibrat
38、ed, the fact that the calculated value is theratio of two measurements eliminates calibration errors as asource of variance. Nevertheless, the following precisionvalues should be considered optimistic (perhaps somewhatlow) but they are more realistic than the previously publishedvalues and should se
39、rve until a proper, multi-laboratory, ILS isachieved.7.1.1 Table 1 summarizes the results of an Internal Labora-tory Study conducted using Test Method F1252 08. To beconservative, the repeatability and reproducibility values in thefollowing sections are based on the largest (worst) percentvalues (Co
40、lumns 5 and 7) found in Table 1.7.1.2 RepeatabilityThe difference between successive re-sults obtained by the same operator with the same apparatusunder constant operating conditions, would, in the long run, inthe normal and correct operation of the test method exceed thefollowing values only in one
41、 case in twenty:Repeatability = 0.15 % of coefficient valueFor example, if a measurement of a sample results in areflection coefficient value of 0.08000, then only one time intwenty should a repeat measurement be different by more than0.15 % of this value (0.08000) or by more than 0.00012.Similarly,
42、 if the sample was measured to have a reflection3Supporting data have been filed at ASTM International Headquarters and maybe obtained by requesting Research Report RR:F07-1009.TABLE 1 Summary of Internal Laboratory Study ResultsSample Angle Degree Avg ReflectCoefficientRepeatabilityReflect. Coeff%
43、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 0.33391 0.00046 0.14 0.00402 1.202A 20 0.34585 0.00037 0.11 0.00272 0.792A
44、 30 0.34839 0.00025 0.07 0.00316 0.91FIG. 4 Rotation of Sample for Polarization CheckReflection data Reflection CalculationsLuminance ofSource (L)Luminance ofReflection offSpecimen (Ls)Reflection ofRotatedSpecimen (Lp)(Optional)Reflection ofStandard(Optional)SpecimenReflectioncoefficient(Ls/L)Polari
45、zationCheck (Lp/K)(Optional)Glass Standard(Lst/L) (Optional)Run 1Run 2Run 3Sample Identification _ Date _Source Identification _ User _Standard Identification _FIG. 5 Calculation of ReflectionF1252 103coefficient of 0.50000, then the repeatability value would be0.15 % of 0.50000 or 0.00075. In other
46、 words, the potentialerror is proportional to the value measured.7.1.3 ReproducibilityThe difference between two singleand independent results obtained by different operators work-ing in different laboratories on identical material would in thelong run, exceed the following values only in one case i
47、ntwenty:Reproducibility = 1.20 % of the coefficient value7.2 BiasThe procedure in this test method has no knownbias.ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly a
48、dvised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, eith
49、er reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This stan
