1、Designation: F 1252 08Standard 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 year of last revi
2、sion. 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 as speci-mens. The
3、 results 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 othe
4、r units 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
5、 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 theangle between the incident light ray and the normal to thesurface (see Fig. 1).2.1.2 angle of reflection (Qr)in the
6、plane 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 Ill
7、uminance 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
8、increase, 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
9、 with 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 define
10、d 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 whichthe reflected light is measured, the thickness, surface quality,and type of material of the specimen, whether the specimen
11、 iscoated, 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 st
12、andard source is determined bymeasuring it 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.1This tes
13、t method is under the jurisdiction of ASTM Committee F07 onAerospace and Aircraft and is the direct responsibility of Subcommittee F07.08 onTransparent Enclosures and Materials.Current edition approved April 1, 2008. Published April 2008. Originallyapproved in 1989. Last previous edition approved in
14、 2002 as F 1252 89(2002).FIG. 1 Apparatus Set-UpFIG. 2 Photometer Field of View1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4. Significance and Use4.1 Reflections from aircraft transparencies of instrumentlights and other cockpit
15、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 significant val
16、ue 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 ratio oftwo lumi
17、nance 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 be used to eva
18、luate 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 tester; itis up to
19、 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 The angle of
20、 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 photometer is not
21、 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 reflected image
22、 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 focus on the
23、 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 than 0.1 %.5.5
24、 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 (forexample 5
25、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 The pivot poin
26、t 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 pivot point
27、(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 photometer at a posi
28、tion 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 frontsurface is at
29、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 source maybe sep
30、arated 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 measurement field. Focus the photometer on2There exists a maximum angle of incidence for which measurements c
31、an 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 as the specimenthickness increases. For most measurements a four inch wid
32、e 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 MeasurementF1252082the image of the source and measure the luminance of thesource reflection using the specimen. Record this value as Ls.6.6 (Optional) Repea
33、t 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 the specimen ea
34、ch 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. 5 to calculat
35、e the reflection.7. Precision and Bias7.1 PrecisionThe remainder of this section refers to anInter-laboratory Study (ILS) that was evidently done at thetime this test method was developed. However, ASTM doesnot have a copy of the ILS in their archives and no currentsubcommittee members have been abl
36、e to locate a copy of thestudy or the results. Therefore, the subcommittee has decidedto conduct an ILS to generate data for a new precision and biassection. Until such time as the new ILS is completed, thefollowing information on precision and bias published in theoriginal test method should be tre
37、ated as provisional. Thevalues reported appear to be larger than what experience withthe test method would indicate.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 nor
38、mal and correct operation of the test method exceed thefollowing values only in one case in twenty:Repeatability = 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 the
39、long run, exceed the following values only in one case intwenty:Reproducibility = 0.0267.2 BiasBias depends upon 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
40、. Scratches on the surface ofthe specimens may affect the accuracy of results.FIG. 4 Rotation of Sample for Polarization CheckF1252083ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standa
41、rd are expressly advised 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
42、 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 International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, whi
43、ch 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 standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,U
44、nited 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), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).Reflection data Reflection CalculationsReflecti
45、on 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. 5 Calculation of ReflectionF1252084
