# ASTM F1316-90 (Reapproved 2013)

Designation: F1316 − 90 (Reapproved 2013)Standard Test Method forMeasuring the Transmissivity of Transparent Parts1This standard is issued under the fixed designation F1316; 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.INTRODUCTIONTest Method D1003 has received wide acceptance as a test method to measure luminoustransmissivity in transparent materials. However, because Test Method D1003 requires criticalalignment of equipment on both sides of the transparency, it is not suited to measuring thetransmissivity of large, curved parts or parts that are installed. In addition, Test Method D1003measures the luminous transmissivity of the material in a direction perpendicular to the surface of thematerial. For the majority of aircraft windscreens, the pilot is not viewing through the transparencyperpendicular to the surface. Since the transmissivity varies as a function of viewing angle the valuesof transmissivity measured perpendicular to the surface do not indicate what the pilot will see whenviewing through the windscreen.For the above reasons this test method has been developed to allow the measurement oftransmissivity of a transparent part at any angle. Since the relative alignment of the equipment itemson either side of the transparency is not critical, this test method can also be used on large, thick, orcurved parts and parts that are already installed.1. Scope1.1 This test method describes an apparatus and procedurethat is suitable for measuring the transmissivity of large, thick,or curved transparent parts including parts already installed.This test method is limited to transparencies that are relativelyneutral with respect to wavelength (not highly colored).1.2 Since the transmissivity (transmission coefficient) is aratio of two luminance values, it has no units. The units ofluminance recorded in the intermediate steps of this testmethod are not critical; any recognized units of luminance (forexample, foot-lamberts or candelas per square metre) may beused, as long as use is consistent.1.3 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. Referenced Documents2.1 ASTM Standards:2D1003 Test Method for Haze and Luminous Transmittanceof Transparent Plastics3. Terminology3.1 Definitions:3.1.1 black reference—a light-absorbing, black material,such as black velvet flocking.3.1.2 photometer—a device that measures luminance asdefined by the spectral sensitivity of the photopic curve.3.1.3 Photopic curve—the photopic curve is the spectralsensitivity of the eye for daytime conditions as CommitteeInternationale d’Elairage (CIE) 1931 standard observer.3.1.4 regulated light source—a light source with electronicfeedback to ensure that its illuminance remains constant overtime.3.1.5 transmission coeffıcient—same as transmissivity.1This 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 Dec. 1, 2013. Published December 2013. Originallyapproved in 1990. Last previous edition approved in 2008 as F1316 - 90(2008).DOI: 10.1520/F1316-90R13.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at service@astm.org. For Annual Book of ASTMStandards volume information, refer to the standard’s Document Summary page onthe ASTM website.Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.1.6 transmissivity—the transmissivity of a transparent me-dium is the ratio of the luminance of an object measuredthrough the medium to the luminance of the object measureddirectly.4. Summary of Test Method4.1 A regulated light source with a relatively large, diffuselyradiating surface area is placed on one side of a transparent partto be measured. A black, light-absorbing reference surface isplaced next to the light source. A photometer is used tomeasure the luminance of the light source and black referencedirectly and through the transparency. The light source readingmeasured through the transparency minus the black referencereading through the transparency is divided by the light sourcemeasured directly minus the black reference measured directly(see Eq 1). This ratio is the transmission coefficient of thetransparency. The black reference surface is used to correct themeasurement from the effects of light scatter due to haze andfrom reflections.35. Significance and Use5.1 Significance—This test method provides a means tomeasure the transmissivity of parts in the field (alreadyinstalled on aircraft) and of large, thick or curved parts thatmay not lend themselves to measurement using Test MethodD1003.5.2 Use—This test method may be used on any transparentpart. It is primarily intended for use on large, curved, or thickparts that may already be installed (for example, windscreenson aircraft).6. Apparatus6.1 Test Environment—It is preferable to carry out this testmethod in a light controlled environment although this is notabsolutely necessary. The transparency should be shaded fromdirect sunlight falling on the surface and a light absorbingblack cloth should be placed in the appropriate reflectiongeometry with respect to the transparency to reduce reflections.6.2 Photometer—Any properly calibrated photometer maybe used for this measurement. It should have a measurementfield that is smaller than the regulated light source to ensureaccurate readings. It is recommended that a small, portablephotometer with a 1° measurement field (or less) be used.6.3 Light Source—The light source should be regulated toensure that it does not change luminance during the readingperiod. It should have a relatively large, diffusely emittingsurface area to permit easy measurement when using thephotometer. The spectral distribution of the light source is notcritical unless the transparency under test has significantspectral peaks or voids. For daylight measurements it ispossible to use a white reflecting surface illuminated bysunlight instead of a powered light source. Care must be takenthat the luminance of the reflective surface does not changeduring the reading.6.4 Black Reference—A shaded, light-absorbing black ma-terial such as velvet may be used to increase the accuracy of themeasurement. This reference must have about the same area asthe light source or reflective material used for the light readingsince the photometer must also measure the apparent lumi-nance of the black reference.7. Test Specimen7.1 Clean the part to be measured, using any acceptableprocedure, to remove any surface contaminants that maycontribute to the loss of transmissivity. No special conditioningother than cleaning is required.8. Calibration and Standardization8.1 The photometer should have the same spectral sensitiv-ity as the eye but since the measurement involves the divisionof two quantities measured by the photometer it is notnecessary that the photometer be calibrated in absolute lumi-nance units.9. Procedure9.1 Place the light source (or white reflective surface) onone side of the transparency such that is can be viewed fromthe other side of the transparency. The transparency should beat the desired angle for measurement. The distance from thelight source to the transparency is not critical but must begreater than 30 cm (11.8 in.) to prevent erroneous readings dueto light scatter and reflections. The distance from the lightsource to the photometer is also not critical but should be shortenough so that the photometer measurement field easily fallswithin the emitting area of the light source. The distance fromthe transparency to the photometer is not critical and may be assmall as 0 cm. The black reference should be placed adjacentto the light source so that it may also be viewed through thetransparency. The light absorbing cloth should be placed nextto the transparency on the opposite side from the light source(see Fig. 1).9.2 If the transparency is subject to direct sunlight, a solarshield should be used to shade the area of the transparency (seeFig. 1).9.3 The photometer is then used to measure the luminanceof the light source and the black reference. These readings aredesignated Lsand Lbrespectively. The light source and blackreference are then measured again but this time viewingthrough the transparency. These readings are Lstand Lbtrespectively. Both the direct measurements and the measure-ments through the transparency should be made at about thesame distance and angle from the light source.10. Calculation10.1 The transmissivity of the transparency is calculatedusing the following equation:t 5Lst2 LbtLs2 Lb(1)3Turk, H. L. and Merkel, H. S., A New Method for Measuring the Transmissivityof Aircraft Transparencies. Technical Report AAMRL-TR-89-044, ArmstrongAerospace Medical Research Laboratory, 1989.F1316 − 90 (2013)2where:t = the transmission coefficient of the transparency,Ls= the luminance of the light source (white surface),Lst= the luminance of light source measured through thetransparency,Lb= the luminance of the black reference, andLbt= the luminance of black reference measured throughthe transparency.The transmission coefficient, t, can be converted to percenttransmission, T, by multiplying by 100. In equation form:T 5 100 3 t (2)10.2 The second term in the numerator in Eq 1 removeseffects due to light scatter or reflections from the measurement.Similarly, the second term in the denominator removes errorsthat arise from the black reference pattern not being completelyblack. See the Appendix X1 for the derivation of this equation.11. Precision and Bias11.1 Four tests were done on a set of nine samples to obtaininformation on precision and bias. The first test was done usingTest Method D1003 for comparison purposes; the other threetests were done using the current procedure. These tests werereproducibility test (using Test Method D1003) at four labora-tories with a total of six devices, repeatability test using onephotometer and one operator for twelve trials, reproducibilitytest using one operator in one laboratory with seven differentphotometers, and reproducibility using one photometer and sixoperators at four different laboratories.11.2 The nine transparent samples included one laminatedsample (2.22 cm (7⁄8 in.) total thickness), three thick (1.59 cm(5⁄8 in.)) monolithic samples, and five thin (0.32 cm (1⁄8 in.))monolithic samples. The samples ranged from about 90 %transmissive to about 15 % transmissive, that includes most ofthe transmissivities that would be encountered in aircrafttransparencies and helmet visors. There is no reason to expectthat thickness of the sample or number of layers would have aneffect on the measurement of transmissivity.11.3 To provide a reference for comparison, the ninesamples were measured following Test Method D1003 at fourlaboratories using a total of six devices, yielding 54 measure-ments. The variance and coefficient of variation (standarddeviation divided by the mean transmissivity times 100 %)were calculated for the six measurements made on eachsample. The variance σ2was 0.214 and the mean coefficient ofvariation was 0.97 %, resulting in a 95 % confidence interval of61.9 % of the transmissivity reading. It should be noted thatthe coefficient of variation was not uniform with respect totransmissivity but tended to be higher for lower transmissivi-ties.11.4 All nine samples were measured using the proceduredescribed herein by a single operator at one laboratory using asingle photometer. The procedure was repeated twelve times,yielding 108 measurements. The variance and coefficient ofvariation were calculated for each sample as noted above. Theestimate of the variance σe2was 0.0115 and the mean coeffi-cient of variation was 0.18 %. The coefficient of variation wasfairly uniform independent of the transmissivity of the sample.11.5 All nine samples were measured with this procedure bya single operator at one laboratory using seven differentphotometers, yielding 63 measurements. The estimate of thevariance σp2was 0.0564 and the mean coefficient of variationwas 0.49 %.11.6 All nine samples were measured with this procedure bya total of six operators at four laboratories using a singlephotometer, yielding 54 measurements. The estimate of thevariance σo2was 0.0467 and the mean coefficient of variationwas 0.35 %.11.7 Considering a typical application of the new procedureto involve different operators in different laboratories usingdifferent photometers, the confidence interval may be esti-mated from the acquired data. The variance of the transmis-sivity measurement, σ2, may be modeled as:σ25 σo21σp21σe2(3)where:σo2= the variance of the operator,σp2= the variance of the photometer, andσe2= the variance of the repeatability error.It is assumed there is no operator-photometer interaction.Substituting the appropriate values into Eq 3 yields.σ25 0.115 (4)The corresponding 95 % confidence interval is then:61.96 3σx¯3100% 561.12% (5)where:x¯ = the mean transmissivity of the samples (0.595).FIG. 1 Geometry of the Transmissivity MeasurementF1316 − 90 (2013)311.8 The preceding information indicates this new proce-dure is slightly more precise than Test Method D1003 since itresults in a tighter confidence interval. The confidence intervalof the new procedure is 1.12 %, versus 1.90 % for Test MethodD1003. Thus if the transmissivity were measured to be 0.50(0 %) the 95 % confidence interval would be 0.494 to 0.506(49.4 % to 50.6 %).11.9 This test method has no known inherent bias. However,it is likely slightly different results will be obtained using thistest method than Test Method D1003. When light is incident ona nominally transparent part the transmitted light is composedof both scattered and unscattered components. The scatteredlight is measured as haze using Test Method D1003. Theunscattered light is the only useful transmitted light for imageformation and visibility. This test method measures almostexclusively the unscattered transmitted light whereas TestMethod D1003 measures a combination of both the scatteredand unscattered transmitted light. It is for this reason that TestMethod D1003 will tend to result in higher transmissivityvalues than this test method for parts that exhibit measurablehaze.11.9.1 The degree of difference depends on the amount ofhaze in the transparent material. Four of the nine samplestested had haze readings in the region of 1 to 2 %. Thesesamples had transmissivity values of 84 to 90 % using