1、Designation: F 1252 89 (Reapproved 2002)Standard Test Method forMeasuring Optical Reflectivity of Transparent Materials1This standard is issued under the fixed designation F 1252; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the
2、 year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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
3、as speci-mens. The results are repeatable without specifying a particularbrand name of instrumentation.1.2 The values stated in SI units are to be regarded asstandard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of
4、the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory 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 thea
5、ngle between the incident light ray and the normal light ray tothe surface (see Fig. 1).2.1.2 angle of reflection (Qr)in the plane of the lightsource, specimen, and photometer, the angle of reflection is theangle between the reflected light ray and the normal light rayto the surface (see Fig. 1).2.1
6、.3 field of view (FOV)the solid angle (degrees) that canbe viewed through the photometer (see Fig. 2).2.1.4 light sourceunless otherwise specified, the NationalInstitute of Standards and Technology (NIST) diffused nonpo-larized Standard Illuminance C light source shall be used. Thelight source size
7、will be such that there will be sufficientoverlap of the front and rear images on the specimen to overfillthe 1 field of view of the photometer. This overlap isillustrated in Fig. 3. (As angle of incidence and specimenthickness increase, the two images will diverge.) If a lightsource other than the
8、NIST Illuminant C is used, it should bespecified and reported as part of the test results.2.1.5 photometerany commercial photometer or photopicfiltered radiometer with a field of view of 1. A model with aviewfinder is recommended.2.1.6 pivot pointthe point in space at which the incidentlight ray and
9、 reflected light ray are to intersect (see Fig. 1).2.1.7 reflectivitythe reflectivity of a transparent specimenis defined as 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 whichth
10、e reflected light is measured, the thickness, surface quality,and type of material of the specimen, whether the specimen iscoated, the spectral distribution of the light source, and thespectral sensitivity of the measurement device. The reflectivity,1This test method is under the jurisdiction of AST
11、M Committee F07 onAerospace and Aircraft and is the direct responsibility of Subcommittee F07.08 onTransparent Enclosures and Materials.Current edition approved Oct. 27, 1989. Published December 1989.FIG. 1 Apparatus Set-UpFIG. 2 Image OverlapFIG. 3 Photometer Field of View1Copyright ASTM Internatio
12、nal, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.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 standard source is determined bymeasuring i
13、t directly with the photometer. The luminance ofthe reflection of the source is then measured off the specimenat 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 aircra
14、ft transparencies of instrumentlights and other 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
15、 is that different brandswill often give significant 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. S
16、ince the reflectivity is defined as the ratio 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 mat
17、erials. Fur-thermore, the test method may be 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 provi
18、sions are offered as an option to the tester; 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 appar
19、atus shall be set up as shown in Fig. 1.5.2 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 source to the spec
20、imen shall equalthe distance from the photometer to the specimen (R). Toensure that the reflection measurement is made over an area ofat least 1.58 cm2(0.25 in.2) on the specimen, the distance Rshall meet the condition:R 5 81.3 6 2.54 cm 5 32 6 1 in. (1)5.4 The minimum surface length across the spec
21、imen sur-face shall be 10.2 cm (4.0 in.).5.5 The testing will be done in a room with no other lightsource besides the specified light source.5.6 A flat black surface (such as black velvet) shall bebehind the specimen during measurement to prevent secondsource reflection.6. Procedure6.1 Allow the lig
22、ht source and photometer to warm up permanufacturers specification.6.2 The 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 p
23、iece ofcardboard. Position the light source at a proper distance fromthe pivot point (5.3).6.3 Locate the photometer at a position equidistant from thepivot point such that the source, pivot point, and photometerare in line (see Fig. 4). Direct the photometer such that its FOVis centered on the lumi
24、nance source. Focus the photometer onthe source and record the luminance L.6.4 Locate the photometer 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 t
25、he pivot point iscentered in the FOV.6.5 Position the desired specimen such that the center offront surface is at the pivot point. Remove any object that mayhave been used to mark the pivot point. Keeping the photom-eter and source fixed, adjust the attitude of the specimen untilthe image of the sou
26、rce completely covers the photometersFOV. Depending on the specimen, the image of the source maybe separated into two images due to reflections from the frontand back surfaces of the specimen. In this case, position thesource such that the overlapping region of the images iscentered over the FOV. Fo
27、cus the photometer on the image ofthe source and measure the luminance of the source reflectionusing the desired transparent specimen. Record this value as Ls.2There exists a maximum angle of incidence for which measurements can bemade. For the apparatus specified, this angle, Qmax, depends only upo
28、n the size,thickness, and index of refraction of the specimen. A thin specimen four inches widewill permit measurements for Q up to 132. Qmaxwill decrease as the specimenthickness increases. For most measurements a four inch wide specimen will beadequate; a larger width may be required for very thic
29、k specimens and/or largevalues of Q.FIG. 4 Apparatus Set-Up for Source MeasurementF 1252 89 (2002)26.6 (Optional) 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. 5).6.7 Steps 6.3-6.6 should be repeat
30、ed a minimum of threetimes for each specimen (varying the location of the reflectionupon the surface of the 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 wish to be identif
31、ied. If so, perform steps 6.3-6.6using the standard specimen. Record the luminance value asLst.6.9 Fill out Fig. 6to calculate the reflection.7. Precision and Bias7.1 PrecisionThe precision of this test method as deter-mined by the statistical examination of the interlaboratory testresults is as fol
32、lows:7.1.1 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 case in twenty:Repeatabilit
33、y = 0.00957.1.2 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 intwenty:Reproducibility = 0.0267.2 BiasBias depends upo
34、n conformance to the condi-tions of the test method. Care should be taken to ensure that thespecimens are clean, the ambient lighting is controlled, and theapparatus is positioned correctly. Scratches on the surface ofthe specimens may affect the accuracy of results.ASTM International takes no posit
35、ion respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibilit
36、y.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM
37、 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 s
38、hown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-8
39、32-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).FIG. 5 Rotation of Sample for Polarization CheckReflection data Reflection CalculationsReflection ofSource (L)Reflection ofSpecimen (Ls)Reflection ofRotatedSpecimen (Lp)(Optional)Reflection ofStandard(Optional)SpecimenReflection(Ls/L)PolarizationCheck (Lp/K)(Optional)Glass Standard(Lst/L) (Optional)Run 1Run 2Run 3Sample Identification _ Date _Source Identification _ User _Standard Identification _FIG. 6 Calculation of ReflectionF 1252 89 (2002)3
