ASTM_F_1252_-_16.pdf

Designation:F125216Standard 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 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 thereflectivity of transparent materials,hereafter known as speci-mens.The 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 other 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 regulatory limitations prior to use.2.Terminology2.1 Definitions:2.1.1 angle of incidence(i),nin 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(r),nin the 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 source,nunless otherwise specified,the Na-tional Institute of Standards and Technology(NIST)diffusednonpolarized Standard IlluminanceAor C light source shall beused.The light source size shall be such that there shall besufficient overlap of the front and rear images on the specimento overfill the measurement field size of the photometer.Thismeasurement field size,and front and back reflected imageoverlap,are illustrated in Fig.2.(As angle of incidence andspecimen thickness increase,the two images will diverge.)Thelight source used shall be specified and reported as part of thetest results.2.1.4 measurement field size,nthe angular extent,indegrees or arc minutes,of the measurement aperture of thephotometer.2.1.5 photometer,nany commercial photometer or pho-topic filtered radiometer with a suitable measurement field size(1 or smaller is recommended).A model with a viewfinder isrecommended.2.1.6 pivot point,nthe point in space at which the incidentlight ray and reflected light ray are to intersect(see Fig.1).2.1.7 reflectivity,adjthe reflectivity of a transparent speci-men is defined as the ratio of the luminance of the reflectedimage of a light source to the luminance of the light source.The reflectivity will depend upon several factors:the angle atwhich the reflected light is measured,the thickness,surfacequality,and type of material of the specimen,whether thespecimen is coated,the spectral distribution of the light source,and the spectral sensitivity of the measurement device.Thereflectivity,as defined here,includes the small amount ofscattered light that contributes to the luminance of the reflectedimage.3.Summary of Test Method3.1 The luminance of the standard source is determined bymeasuring it directly with the photometer.The luminance ofthe reflection of the source,from both the front and backsurfaces of the specimen,is then measured off the specimen ata specified geometry.The luminance of the reflection is dividedby the luminance of the source to obtain the reflectivity of thespecimen.4.Significance and Use4.1 Reflections from aircraft 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.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 of1This test 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 1,2016.Published April 2016.Originallyapproved in 1989.Last previous edition approved in 2010 as F1252 10.DOI:10.1520/F1252-16.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 two luminance measurements and does not depend on anabsolute measurement,dependence upon the accuracy of thecalibration of the measuring instrument is reduced.4.3 The test method may be used to objectively compare thereflection characteristics of various transparent materials.Furthermore,the test method may be used to evaluate