Interlaboratory Comparison of Measurements of the Spectral Irradiance from Fluorescent and Incandescent Lamps: a Report

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<ul><li><p>Interlaboratory Comparison of Measurements of theSpectral Irradiance from Fluorescent andIncandescent Lamps: a ReportC. L. Sanders and C. W. Jerome</p><p>A comparison of spectroradiometric measurements has been completed for the wavelength region from300 nm to 800 nm. The measurement procedures and results obtained in eighteen laboratories are de-scribed. The results are considerably better than those in earlier comparisons. Conclusions regardingprocedures to be avoided are given. Without special precautions 450 illumination on the diffuse receivermay cause serious errors. Normal illumination on a plane or a spherical receiver is better. The power inthe spectral lines was inaccurately measured by Rossler's method.</p><p>IntroductionAt the CIE meeting in Washington in 1967 a sub-</p><p>committee on spectroradiometry was established byCommittees E1.2 Photometry, E1.3.1 Colorimetry,and E1.3.2 Color Rendering. A summary of the pur-pose of the subcommittee, compiled following aquestionnaire to interested people, was as follows:</p><p>1.1 To specify a simple but satisfactory proce-dure for spectroradiometry of continuous, line, andmixed sources of energy. The method should be ap-plicable to measurement of spectral radiance, irra-diance, and radiant flux.</p><p>1.2 To follow this method of spectroradiometry inorder to test the reproducibility of the results whenthe method is followed in different laboratories tomeasure spectral irradiance.</p><p>1.3 To use also the routine method of the partici-pating laboratory and to report the differences in re-sults and in the methods and to provide, if possible,an explanation for the differences.</p><p>1.4 To summarize all such measurements andanalyses and to estimate the error, if any, which islikely to be caused by following any specific proce-dure.</p><p>1.5 To state procedures that should not be usedand to provide the reasons why they should not beused.</p><p>C. L. Sanders is with the Radiation Optics Section, Division ofPhysics, National Research Council of Canada, Ottawa KlA OS1;C. W. Jerome is with the Lighting Products Division, SylvaniaLighting Center, Danvers, Massachusetts 01923.</p><p>Received 2 April 1973.</p><p>1.6 To establish the different accuracy require-ments of spectroradiometry when the results are tobe used for different specified applications. Theseare to include photometry, colorimetry, color ren-dering, and any other unique application.</p><p>As part of its task the subcommittee undertook in1969 and completed in 1971 an interlaboratory com-parison of measurements of the spectral irradiancefrom fluorescent and incandescent lamps.</p><p>Table I shows the spectral irradiances that were tobe compared. Columns 2 and 3 show, respectively,the values. for incandescent and fluorescent lamps.Column 4 shows the ratio that was to be measuredat wavelengths from 300 nm to 800 nm at 10-nm in-tervals. The ratio varies from 0.13 to 0.001. Thespectral response of most detectors is low at 800 nmcompared to the response at 450 nm so the measure-ments provide a severe test of linearity and of straylight in the instrument.</p><p>Eighteen laboratories compared three lamps ofeach type in order to see how well spectroradiometricmeasurements agree when stable fluorescent lampswere measured under specified conditions usingstandards of spectral irradiance that were all cali-brated against one standard.</p><p>Replies from each laboratory to a questionnaireabout procedures and equipment were studied tofind causes for discrepancies in the measurements.Discussion and correspondence has resulted in elim-ination of some of these causes. As a consequence ofthe comparison the subcommittee is in a better posi-tion to recommend the precautions to be taken andthe methods to be followed for spectroradiometrywith a given required accuracy. The preparation ofa committee document on principles of and proce-dures for spectroradiometry will take considerable</p><p>2088 APPLIED OPTICS / Vol. 12, No. 9 / September 1973</p></li><li><p>FluorescentpW-cmn2nm-1</p><p>0.000070.00025'j.001590.006570.016280.02750. 03390.03850.04410.05130.05950.07010.08180.09750.11350.12880.13850. 14370.14420.14340.13920.13730.13520.13000.12080.11020.10190.09570 .09090.08630.08260 .08040.08640.10040.08630.11840.15570.07600.04450.03540.02760.02270.01850. 01530.01290. 01080.00920.00780. 00620.00520. 0044pW.*CM- 2</p><p>0.0940 .0100.3860.7301.0001.0 0840.304</p><p>Ratio(4) = (3)/(2)</p><p>0.0160. 0040. 0180.0570.1060.1380.1340.1230.1150.1120 .1110. 1100. 1110.1150.1180.1180. 1130.1060. 0960. 0880.0780.0710. 0640.0580.0500.0420.0370.0320.0290.0260.0240.0220. 0220.0250.0210. 0270.0350.0160. 0090. 0070.0050.0040.0030.0030.0020.0020.0020 .0010. 0010 .0010. 001</p><p>Note: The top figure in the right-hand column(0.016) should read 0.002.</p><p>time. In the interval a summary of the results isgiven below to aid those involved in spectroradiome-try in deciding how reliable their measurements maybe if certain precautions are taken or to inform thoseusing spectroradiometric measurements how reliablethe data provided are likely to be.</p><p>Organizational ArrangementsThe National Research Council aged and made ir-</p><p>radiance measurements on all tungsten-halogen</p><p>lamps and on the fluorescent lamps for operation at60 Hz. The Sylvania Lighting Center made mea-surements on all fluorescent lamps sent to the labo-ratories using 50 Hz. All lamps were measured in.these coordinating laboratories before and after thefirst measurements in the participating laboratories.The persons and laboratories participating in thiscomparison were the authors, as coordinators of the60- and 50-Hz measurements, respectively, and thefollowing:G. Bauer and K. Bischoff,Physikalisch-Technische</p><p>Bundesanstalt,Bundesallee 100,33 Braunschweig, Germany.</p><p>H. D. Einhorn,Dept. of Elect. Engineering,University of Cape Town,Private Bag, Rondebosch,Cape Town, South Africa.</p><p>W. Heaps,Macbeth Corporation,P.O. Box 950,Newburgh, New York 12550,U.S.A.</p><p>B. Jewess and M. Halstead,Thorn Lighting Limited,Research &amp; Engineering Labs.,Cambridge House,Great Cambridge Road,Enfield, Middlesex,England.</p><p>C. J. Kok and M. C. Boshoff,Precise Physical Meas. Div.,National Physical Res. Lab.,P.O. Box 395,Pretoria, South Africa.</p><p>J. R. Moore,National Physical Laboratory,Teddington, Middlesex,England.</p><p>Leo Mori,Toshiba Research and</p><p>Development Centre,Tokyo Shibaura Elec. Co. Ltd.,Komuka, Kawasaki 210,Japan.</p><p>L. Morren,Laboratoire Central</p><p>d'Electricit6,1640 Rhode St-Genese,</p><p>Belgium.</p><p>M. Nonaka,Central Research Laboratory,Hitachi Limited,Kokubunji, Tokyo, Japan.</p><p>Dr. Nundel and B. Fisher,Deutsches Amt fur Messwesen</p><p>und Warenprufung.,108 Berlin,Niederwallstr. 18-20,Germany.</p><p>J. L. Parascandola,Durotest,2321 Kennedy Boulevard,North Bergen, New Jersey 07047,U.S.A.</p><p>Magda K. Poppe,United Incandescent Lamp &amp;</p><p>Electrical Co. Ltd.,Budapest, IV,Vaci ut 77,Hungary.</p><p>F. Rotter,Bundesant fur Eich und</p><p>Vermessungswesen,Arltgasse 35,A-1160 Vienna, Austria.</p><p>R. Saunders,Room B 308-Met,Photometry Section,Institute for Basic Standards,Washington, D.C. 20234,U.S.A.</p><p>J. Schanda,Research Institute for Technical</p><p>Physics of the HungarianAcademy of Sciences,</p><p>Ujpest 1, PF 76,Budapest, Hungary.</p><p>J. Williams,Opcalite Inc.,2110 South Anne St.,Santa Anna, California 92704,U.S.A.</p><p>Three lamps of each type were sent to the labora-tories the first time but one out of three of the tun-sten lamps was retained at NRC after the repeatmeasurements. The final measurements were madeat the participating laboratories. The tungsten-</p><p>September 1973 / Vol. 12, No. 9 / APPLIED OPTICS 2089</p><p>Table I. Representative Spectral Irradiance of Incandescentand Fluorescent Lamps Used in Comparison, and Ratio of</p><p>Fluorescent to Incandescent LampsIncandescent</p><p>VW-cn 2 n- 1</p><p>0.0450.0620.0860.1160.1540.2000.2520.3140.3830.4590.5430.6350.7340.8470.9641.0921.2221.3561.4951.6391.7881.942.102.262.432.602.782.963.143.323.503.683.854.024.194.364.504.654.794.925.055.205.365.515.665.795.885.966.036.106.15</p><p>nm</p><p>3003103203303403503603703803904004104204304404504604704804905005105205305405505605705805906006106206306406506606706806907007;10720730740750760770780790800</p><p>313334365405436546578</p></li><li><p>halogen lamps retained at NRC will be used to alignthe spectral irradiance scale used in this comparisonwith the mean scale that will result from an inter-comparison of national irradiance scales that is beingcoordinated by Yoshie of the Electrotechnical Labo-ratory, Tokyo, Japan.</p><p>Experimental Procedure and Lamps UsedThe fluorescent lamps, donated by Macbeth Cor-</p><p>poration, were of high color-rendering index (about92) and had a correlated color temperature of ap-proximately 8500 K. A magnesium germanate phos-phor produced a pair of peaks in the red part of thespectrum. The lamps were 40 W, 1200 mm long by38 mm diameter.</p><p>The fluorescent lamps were aged for 550 h in ordi-nary open-grid lighting fixtures using rapid start bal-lasts. They were measured after 500 h and 550 h toconfirm their stability. The final measurements atall laboratories were made using reference ballastsmeeting the specifications in the InternationalElectrotechnical Commission Publication IEC 82.The irradiance was to be measured in a plane at 66cm from a 25.4-cm by 5-cm aperture placed 5.1 cmfrom the center of the fluorescent lamp. The lampswere operated at a fixed current of 0.430 A. Thetotal harmonic distortion was less than 3% from thepower supplies used.</p><p>The standard lamps used were tunsten-halogenlamps of the type GE 6.6A/T4Q/1CL. These are200 W with coiled-coil filaments and have bare wireconnectors. They were operated vertically and posi-tioned 43 cm from the plane where the irradiancewas to be measured. The lamps were aged and se-lected in the factory. They were purchased by NRCand were aged at NRC for a further 25 h. Afterbeing measured some were aged a further 25 h toconfirm that they would not change during the com-parison. Ageing and subsequent operation was at acurrent of 6.5 A. Operation on ac or dc was option-al.</p><p>The method of receiving the irradiance in the irra-diated plane was left up to the individual laboratory.Two methods were used: (1) a plane diffuser ofpressed MgO, MgCO3, BaSO4, or ground quartz,and (2) an integrating sphere with its entrance aper-ture located in the measurement plane. In five labo-ratories, the plane diffuser was illuminated at 00 andviewed at 450 by the spectroradiometer, i.e., 0/45.In two cases the inverse system, 450/00, was used.The arrangement 450/450 was used by five laborato-ries. A sphere used by five laboratories was viewedso that no directly reflected radiation entered themonochromator, i.e., 0d. One laboratory used aquartz diffuser in the transmitting mode 00/00.</p><p>The temperature 25 i 0.50C was specified for op-eration of the fluorescent lamps. Some laboratoriescould not meet this condition and were forced tomeasure at temperatures in the range from 2C to360C. The temperature was to be measured at 15</p><p>2</p><p>wad0crIj.z2</p><p>0</p><p>wF</p><p>16</p><p>12</p><p>8</p><p>4</p><p>0</p><p>-4</p><p>-8</p><p>-12</p><p>-16</p><p>0 1 2 3 4 5 6 7 8 9 10 11 12 13 1415 16 17HBW AT 660nm</p><p>18 19 20</p><p>Fig. 1. Percent error at 660 nm vs half-bandwidth (HBW) ofmonochromators for individual laboratories' average values. Av-erage of seven national laboratories was taken as standard.</p><p>HBW was estimated from replies to questionnaire.</p><p>cm from the lamp center in the same horizontalplane but not all laboratories measured in this man-ner. Continuum measurements were limited to300-800 nm at 5-nm or 10-nm intervals. The sevenHg lines at 313, 334, 365, 404.6-407.7, 435.8, 546,and 377-579 nm were measured. The method andequipment actually used was reported by each labo-ratory. A summary was made of the reports andwas used in drawing conclusions about the causes ofdiscrepancies.</p><p>The monochromators used were calibrated byusing at least Hg lines, but mostly by using linesfrom a number of elements. Some of the laborato-ries checked for wavelength calibration in each mea-surement session using one or more Hg lines. Singleor double monochromators with glass or quartzprisms, gratings, or grating-prism combinations wereused. In spite of the care taken in wavelength cali-bration there was evidence of wavelength errors inmeasurement of the red phosphor peaks. Thesemeasurements may also be seriously affected by thebandwidth of the monochromators used, which var-ied with wavelength for most prism instruments. Asshown in Fig. 1, the bandwidths used at 660 nm werein the range from 1.1 nm to over 10 nm, the meanbeing about 6 nm. The number near each point isthat of a laboratory in the comparison. Laboratories5, 9, and 19 made measurements with narrower band-widths but adjusted the data to give a 10-nm band-width at 660 nm.</p><p>All laboratories used a photomultiplier as the de-tector. One used PbS above 700 nm. Most PMT'shad S20 surfaces. Most laboratories checked thelinearity of their systems. One reported significantstray light of several percent in the red above 700nm. One laboratory reported that hysteresis causedthe far red part of the spectrum to be high in its firstset of measurements.</p><p>2090 APPLIED OPTICS / Vol. 12, No. 9 / September 1973</p><p>I 1 * 2 P l I I I I I I I I I I I I</p><p>21\_R * *18QP</p><p>8GP</p><p>10PG. ..7QPOP*7GR</p><p>*13GP</p><p>0 I -9GR</p><p>*3GR I GP .5QP</p><p>.4QPI I I I I I I I I N I I I I I I</p><p>. . .. . . . . . l. l. l . .l .l l </p><p>Ro cv</p></li><li><p>Analysis</p><p>It should be noted at the outset that the data asfirst received from the laboratories contained somemeasurements that were in error because of mistakesin calculation that were later corrected. The stan-dard deviations noted in this report are therefore lessthan would be obtained if no opportunity were givenfor correction of data.</p><p>As results were received from the participatinglaboratories the following two assumptions appearedjustified and were used in the analysis of the data.</p><p>(1) There was an insignificant difference betweenthe relative spectral irradiance of the individual fluo-rescent lamps used in this intercomparison. Thiswas indicated, among other ways, by the fact thatthe standard deviation of an individual lamp mea-surement of spectral irradiance, determined by mea-suring sixteen fluorescent lamps at NRC, was onlyfour-tenths that of the standard deviation of mea-surements at all the participating laboratories. Ifone looks instead at the range of chromaticity coor-dinates at NRC compared to those for all laborato-ries, one finds NRC values on sixteen lamps for an18-day period in 1970 covering the area enclosed bythe solid curve of Fig. 2. The dashed curve of Fig. 2encloses the spread of measurements at NRC overthe period 1968-1972.</p><p>(2) There was an insignificant difference betweenthe results at 60 Hz and 50 Hz. This was shown byJerome's measurements at the two frequencies andby an insignificant difference between the means ob-tained by laboratories at the two frequencies.</p><p>The absolute value of spectral irradiance variesmuch more than the relative value. There was alarge variation in the reported relative irradiances ofthe mercury lines. This is not surprising, since it isrecognized that these line irradiances in a fluorescentlamp are strongly affected by mercury vapor pres-sure, which is affected by temperature and drafts.Normal spatial varia...</p></li></ul>

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