# AC 20-74: Aircraft Position and Anticollision Light Measurements - Type: Advisory circular (guidance, not mandatory unless a rule or AD requires it) - Status: Current - Approved: July 29, 1971 - Family: AC 20-74 - Pages: 45 - FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/0410AB09B4A7057D862569AE006D35D1.0001 - Page: https://openairdocs.org/ac/20-74 ## Versions - AC 20-74 (Current), approved Jul 29, 1971 ## Text ### Page 1 AC NO: 20- 14 DATE: 29 July 1911 • ADVISORY -~­ ~ CIRCULAR• AJ;BCB,AfI f9§JIJQN 4liP ANTTCQL1jISTQN LJQHT MEA§YBEMENI§ **DEPARTMENT OF TRANSPORTATION** FEDERAL AVIATION ADMINISTRATION Initiated by: FS-130 ### Page 2 29 .July 1971 AC 20-74 **FOREWORD** 1. PURPOSE. this advisory circular contains useful information concerning mea1urementa for intensity, covering and color of aircraft position and anticollision lights. 2. 'REFERENCES. Federal Aviation Regulations FAR. 23.1385 through 23.1397 and 23.1401. FAR 25.1385 through 25.1397 and 25.1401. FAR 27.1385 through.27.1397 and 27.1401. FAR 29.1385 through 29.1397 and 29.1401. Advisory Circular AC 20-30A. **3. BAQCGROUND.** a. this advisory circular has been developed as a reference for those concerned with data on measurements of aircraft position and anti• collision lights. Light measurement is quite complex, and users of this advisory circular will have various degrees of experience and training. Por these reasons, chapter one contains educational and reference material on the properties of light. It includes a description of ..light and discusses the general parameters • b. Ch.apter two includes information qn types of measurements·and descriptions of the equipment used to make them. c. Chapter three ia devoted to discussions on measurement data. First, the Federal Aviation Regulations are shown by pictorial representa· tions. Following this, measurement data considerations are given including the precautions which should be observed when making measurements. d. The appendices include a 1101sag of terms, a conversion table, a biblioaraphy and a discussion of tristimulus colorimetry as applied to aircraft position and anticollision ligt.t measurements. Service ### Page 3 ...· 29 J'uly 1971 TABLE OF CON'lENTS **LIST OF ILLUSTRATIONS** LIST OF TABLES CHAPT!lt 1. PROPER.TIES OF LIGHT 1. General 2. Intensity 3. Color CIIAPTEB. 2. MEASUl!NEN'l CONSIDBIATIONS 4. General 5. Inte-sity 6. P0lor ~ 7. Teuaperature Effect• 8. General 9. Position Light Data 10. Anticolllslon Liaht Data APPENDIX 1. GLOSSARY OF TERMS APPENDIX 2 • PBOTCJmTlUC TERMS APPENDIX 3. TllISTIMtJLUS COLOR.IMB'l'R.Y AND AVIATION LIGHTS APPENDIX 4. BIBLIOGIAPBY AC 20· 74 Page iii V l 2 2 6 13 13 13 16 19 21 21 21 24 (2 pages) l (1 page) l (2 pages) l (2 pages) 1 ### Page 4 29 .July 1971 AC 20- 74 LIST OP ILLUfflATIONS Ill!& The Visible Spectrum Standard •Observer Lum1iaou1•Efficiency Curve (C.I.E.) Intensity and Illumination Spectral Tri1timulua Value• According to the 1931 C.I.E. Standard Obaerver C.I.B •. ChrotM.ticity Diagram Strip Recording of Pla1h Poaition.Ligbts, Minim&pa tnten11ty in the Horisontal Plane Position Lights, Minimum lntensities in Vertical Plane• Anticolliaion Light•, Minimum tntenaity in Vertical Plane Typical Borisontal Calldlepower Distribution•Poaition Light Typical Vertical c:anctlepowr Distribution•Poaition Light Vertical Distribution of Rotating Beacon Time vs. Intenaity curvea o0 ancl s0 for Rotating Beacon Time va. Intenaity • 2Q 0 for Rotating Beacon Typical Plashtube Measurement Data Sheet rICURE 1.1 1.2 1.3 1.4 1.5 2.1 3.1 3.2 3.3 3.4 3.5 3.6 3. 7 3.8 3. 9 PAGE - 1 3 5 7 10 15 27 28 29 30 31 32 33 34 35 Page iii(and iv) ### Page 5 29 July 1971 AC 20-74 LIST OF TABLES PACE!!!!::! ~ 4 Spectral Luminous Efficiency, V(A) 1.1 8 Computation Form 2.1 .17 Spectral Tristimulus Values 1.2 Page v (and vi) ### Page 6 •••• AC 20-7429 July 1971 CHAPTEI. 1 PllOPEB.'IIES,OF LIGHT 1. GEND.AL. Light is visually evaluated radiant energy •. Like other forms of radiant energy, light travels through space at a constant velocity of 300,000 1 000 me..ters per second. Light energy may be considered as having a sinusoidal wave form, stimulating vision only over a narrow band of wavelengths (Fig. 1.1). Within this band, the amplitude affects the vuual sensation of brightneS8 and the wavelength, the visual sensation of hue. The longest waves produce a sensation of red, and the shortest a sensation of violet. By definition, white occurs when all visible wavelengths are combined in equal amounts. The appearance of white, however, may be produced when certain critical ones are combined. If the light covers a narrow band of wavelengths, a certain hue is seen. Black is usually treated as the absence of sti111Ulation. The wavelength of light may be expressed in micrometers (~m), equal to 10-6 meters, in nanometers (am), equal to 10-9 meters, or in angstroms on, equal to 10-10 •tera. · WAVELENGTH IN METERS 10-1 104 10• lt&OIO WAVII •ttR&•ltl'.D •-c••o•• CIRCUITS ......I ......I ....I ... ....I .... I .... .... I ' .... I .... **I VISIBLE SPECTRUMI ' ',....** 700 I .... < ..HN Yl&.LOW Olt&N& I II..,." .... 400 500 100 • WAVELENGTH IN NANOMETERS 1.11!,VISIBLE SPECTRUM !'igure 1.1 t--1--~-..,..,.--,,'--- uu••­v10Ln .t.-,---4..--f..-__,J--...___,,..J-_--4 ...,. Chap l Page 1Par 1 ### Page 7 29 July 1971AC .20• 74 ,,.,,,.. ....The sensitivity of the eye, bovever, varies withia. this visible spectrum. Radiant energy at.differeut wavelengths produces varying sensations of brightness even though the amount of energy received is the same at each wavelength. Figure 1.2 and Table 1.1 shaw that the eye is twice as sensitive to a yellow-green of 555 nanometers, as it is to a green of 510 nm. This cur.-e is referred to u "spectral sensitivity of the human eye" or "luminous efficienc.y". When the intensity of colored lights is measured, this variable sensitivity of the eye must be taken into consideration. In other words, a red light IILISt be auch higher in power to appear equally as bright as a green light. The detecting device, therefore, 1111st be corrected for the response of the staa.dard observer if the reading is to indicate luminous (visual) output. · The numbers associatedwith Figure 1.2 and Table 1.1 are referred to as "spectral luminous efficiencies". It should be remembered that lumens and candelas are associated with visible light, and as the sensitivity of the eye decreases, so does the amount of lumens for the same radiant pover. This is evidenced in the conversion from watts to lwaens: luminous flux in lumens • 680 V().) times the radiant flux in.watts. 2. INTENSITY. The luminous flux being emitted from a point source, if the light is ·emitted equally in all directions, may be represented by a sphere. Light flux is rate of flow of visible energy. The basic unit of flux is the lumen which by definition is equal to l/4w times the total flux emitted by a uniform point source of one candela. The flux emitted by a point source per unit solid angle (steradian) is called intensity. A steradian is defined as that solid angle originating at the center of a sphere and subtending an area on the sphere surface equal to the square of the sphere radius. Intensity is measured 1a. lumens per steradian, and a uniform point source equal to one candela has an intensity in every direction of one lumen per steradian. Intensity in a given direction is usually expressed in candelas and is often called candlepower. The luminous flux density received on a surface (illuminance) varies with the intensity of the source, and inversely as the square of the distance from the source to the surface. Illuminance is expressed in lumens per unit area or footcandles. Figure 1.3 shows that as the distance from a source increases, one lumen is spread over increasing areas, and the illuminance decreases. The relation of illuminance to distance from the source is referred to as the "inverse square law". The illuminance from a given source varies inversely as the square of the distance from that source. Doubling the distance causes the illum:inance to decrease to one fourth. As measurements of a light source are usually done with instruments which measure illuminance, the distance ai.st be known before the intensity of the source can be determined. In other words, footcandles times the distance squared gives candelas. For example, if a footcandle reading of 10 is measured at 10 feet from the source, the intensity is 1000 candelas. Chap 1 Par 1 Page 2 ### Page 8 29 July 1971 AC 20-74 ,( -­> • >­u 2 LIJ - u I&.- 0.6 I&. LIJ u, :, 0 z 2 - 0.4 :,_, _, ct a: t-u LLI G.. Cl) Chap 1 Par 2 ,.o 0.9 0.8 0.1 0.5 VIOLET BLUE GREEN YELLOWi I I I I ,r \ I 1 \ I \ I \ \ REO .. 0.3 0.2 O.t J I \ I \ V \ L/ '­0 380 420 460 500 540 580 620 660 700 740 WAVELENGTH OF RADIANT ENERGY IN NANOMETERS STANDARD-OBSERVER LUMINOUS EFFICIENCY CURVE ( C.1.E.) Figure. 1.2. ### Page 9 AC 20- 74 29 July 1971 1931 C'.I.!. STANl>AlU) OBSP.B.VEB. **WAVELENGTH** NANOMETEIS 380 390 400 410 420 430 440 450 460 470 480 490 500 510 S20 S30 540 sso 560 570 Page 4 SPECTllAL LUMINOUS WAVEI.Blln'B EFFICIENCY, V(l) IWICltBTDS 0.0000 S80 0.0001 590 0.0004 600 0.0012 610 0.0040 620 0.1116 630 0.0230 640 0.0380 650 .. 0.0600 660 0.0910 670 0.1390 680 0.2080 690 0.3230 700 O.S030 710 0.7100 720 0.8620 730 0.9540 740 0.99SO 7SO 0.99S0 760 0.9520 770 SPECTRAL LUMINOUS EFFICIENCY• Table 1.1 SPBCTllAL LUMINOUS El'PICIENCY, V (),) 0.8700 0.7570 0.6310 O.S030 0.3810 0.2650 0.1750 0.1070 0.0610 0.0320 0.0170 0.0082 0.0041 0.0021 0.0010 o.ooos 0.0003 0.0001 0.0001 0.0000 V00 Chap 1 Pu 2 ### Page 10 29 .July 1971 AC 20- 74 .----INTENSITY •I CANDELA,= I L:.UMEN/STERADl.ff ~t----------lMETER ________ ..,. ........,_____ IFT. ___....., . I CM AREA=ICM 1 ILLUMINANCE• I LUMEN/CM 1 AREA:t Fll IL LUMINANCE: I LUMEN/FT 1 AREA= I METERt ILLUMINANCE a f LUMEN/M 1 INTBNSITY AND ILLUMDIATION Figure 1.3 Fluhing light• are u1ed exten1ively a1 1ignals and warnings because of their superiority ira. attractuag attention. Becauae of thia characteristic, flashing beacoa.e were eatabliahed •• the required lighting for anticollision light8. These beacona are of Hveral types: rotating, flashing incandes­ cent. oscillating and gu discharge (strobe). When a light aignal cOQ.lists of separate flashes, cile maximum intensity during the flash must be greater than the inteueity of a steady light to have the sam apparent inteneity. It is convenient to evaluate flashing light1 in terms of their EFFECTIVE INTENSITY, I 8 or EFI, the intensity of a eteady light which will appear equally bright when viewed at threshold, and is expressed in candelas. Chap 1 Par 2 Page 5 ### Page 11 29 .July 1971 A.C 20-74 Current airworthiness requirements for aircraft anticollision lights specify the following equation (known as the Blondel Rey equation) for the computation of effective inteu.eity:.,.,.. where: le• effective intensity I(t) • instantaneous intensity as a function of time t2 - ti• flash time interval (seconds) The maximum computed value of•-effective intensity is obtained when t2 and t1 are chosen so that the effective intensity is equal to the instantaneous intensity at tz and t1. For short time flashes, t2 ­ t 1becomes insignificant compared to 0.2 seconds, and the total flash is intearated. Short-duration flashtube lights have been used primarily as supple­ mentary lights. Since flashtubes in general produce relatively small proportions of. red light, about 90 percent of the light is lost in passing it through a red filter. Therefore, in order to use this source for an anti-collision light, it is necessary to operate them at higher energy levels than has been comDOn in the small supplementary lights. 3. COLOR. The sensation of color is closely related to the wavelength of light .and varies with the individual and the conditions of viewing. Usually a color is said to have three psychological c0111ponents: !!!:!!., (red, blue, orange, etc.), brightness, and saturation (the amount a color differs from a grey of the same brightness). A measure of hue, sufficiently reliable for signal-color specification, is the wavelength of the part of the spectrum required to be mixed with the equal-energy(white) source to produce the color; this wavelength is called the dominant wavelength of the color. -Saturation ia satisfactorily specified by the ratio of the distance on the CIE chromaticity diagram (See Figure l.S) from the equal-energy point to the color point, to the distance from equal-energy point, in the same direction, to the spectrum locus. This ratio is called purity. Chap l Par 3Page 6 ### Page 12 29 July 1971 AC 20•74 It can be shown that any color can be matched by combining three properly choeea. colors called pr111111ry colors. :If a colored sample is placed in OGe half of a photo11etric field. a mixture ~f three primary colors such as red. green. and bbe, in the other half of the field can be made to match the colored sample to the satisfaction of the eye. This is done by varying the relative brightness of the three pdury colors. A problem with this method is that the matching judgment of one obaerver cannot be taken as representative of the average person: Only when a large number of observers are used in each experi•nt can consistent values be obtained for the relative brightne88 of primary colors required to match any given color. In order to avoid this difficulty, the tristimulus method was revised and standardiHd. 'ftlree primary colors were agreed upon; thea., by expert•nta with a number of normal observers, standard values for the relative amounts of each primary color were established to match each wavelength in the visible spectrum. These numbers were associated with.a "standard observer". With these values made available in 1931 by the COllliaaion Internationale de L'Eclairage (CIE), a more objective and ecoaom.cal teclmici\\e is available to specify color. Figure 1.4 is a graphical presentation of the relative amounts of each primary color required to •tch any wavelength. Standard notation for these functions is: i for the red primary. y for the green primary. and z for the blue primary. It should be noted th.at the f function has been adjusted to correspond to the luminous-efficiency function {Figure 1.2). Table 1.2 shows the values of these functions in tabular form. eoo eoo ~nm SPECTRAL TRISTIMULUS VALUES ACCORDING TO THE 1931 CIE STANDARD OBSERVER Figure 1.4 Chap l Page 7 Par 3 ### Page 13 •• •• TAe 1951 CIE _,ta,atlanl ol>aerver ,; Spectral trl1tlmulua TalUH of MUAl•tDUff IPfftral trt,t1mulu1 nlu11 or equal-entrn NWa•t· 1peetrum . 1peetrumwu1;lea,rth, ...... 0•- ., ....T -• 7 ~ .• • .. IH 0.0000180 . o.oou o.ooa 180 O.tlO 0.8100 0.0011.0001.0022 1811 :: .t1H .81113.0101 ....,.0001.00t2 .020 1110 .TITO.0002.OOT8 .OH u::,Ill .,... :331& .ooo,too .0143 .08'19 800 1.0821 .8110tOI .0000.0232 tOI t.otlll·1102 .13ee :gtlO .0435 .0012 • 01: .I 80:10 .000tH .one .0022 .111 o. 38t .ta1~ .0002t20 .Utt .OOtO ,ll '·Ur.MIi ... •• 10 .0002.,,421 .tu8 .0011 1.0191 .TIH .1210 .0001.2839 .out l.1858 eao410 .HH .2810 .0000t I .1285 .0118 1.1210 Ill .Hit .2110 .0000.Ital .0210 UtTl MOtJO ,tt1t ,1110t I .Hat .02111 1.182' HI .1908 .II 2 • 0 no .1382 .0180 U121 ... 1 ·=·.0000·A:10,1187411 .Ot80 Uttl .·1l 811 .te .0000teO .lt08 .oeoo 1.880 fl8 .Utt .0810 .0000t81 .2511 .0739 1.0281 tel ,1212 .OU8t10 .ltllt .0810 1.2878 t10 .OITt .0320 :=tTI .H21 .1128 1.ot19 eta .0281 ,0000.oea3tlO .091UI . 1390 0.8110 . eao .OITO ,0000.3:etH .01180 .1893 ,81 2 8H .121 .0111tlO .2080 ,4812.g120 810 .0221 .008tH • UT .2588 .aaaa 811 ;0118 ,0011 :II.100 .OOtl .1230 .2120 TOO .out .oou .0000IOIJ .002' .t073 TOG.2121 .0029 ,0000.3311IUO .0093 .1030 ,108 TIO . 158 .0000.3321118 .8082 ,1117 TH.0201 ,OOtl . ll ,00001120 .083 .1100 ,OTII TIO .0021 .0010 ,0000 .1098 ,T93202g ,OIT8 1211 .0020 .0007.Hllll .8820 .Ot22 180 .OOH .0005 :smIla .2257 .9H9 .0288 TH .0010 .OOOt .0000HO .29ot .911t0 .0208 TtO .0007 .0003HI .1111 .8803 .out Tt5 .0001 .0002 :=HO .43U .1910 .0081 TIIO .0003 .0001 .0000HI .11121 1.0002 .00111 TOIi .0002 .0001 .00001180 .Htl O.HIO .0039 T80 .0002 .0001 .0000.,7H .0027.g78e 1811 .0001 .0000 .0000H& . 1121 . 120 .0021 170 .0001 .0000 .0000 .HH11g .gu5 TTI.gg1e .0000 .0000Ill • 103 .8100 • 1T TSO .0000 .0000.... := -­- . ­Total, _____ 21.1713 2l.17lt 21.ITU **SPECTRAL TRISTIMULUS VALUES ..** Table 1,2 \ ### Page 14 29 July 1971 AC 20-74 Capital lettere x. Y, aad. Z have bean u•ipe.d u o.otatioa. for·the aaou.a.te of tbe three pri•riea required to viaually utch a color containing multiple wavelength•. Thue valuea can be plotted ~raphically if the following traneformationa are m.ade: x • X (2) y. y . (3) z. z (4) X+1'+Z X+Y+Z X+Y+Z where X, Y, and z are the amounts of the three primaries ana x, y, and z are the "c.hro•ticity coordinates" in the CU system. The horizontal of the graph becomes x and the vertical becomes y; z may be obtained from the relationship x + y + z • 1. Such a graph, shown in Figure 1.S, 18 called a chromaticity diagram. Any color may be located 011 the diagram. by specifying its chroma.ticity coordinates. The colors used ·for lighting of aircraft are shown with the limits ae established by the airworthiness regulations. On this diagram, there is a central white point marked 1,.where X • Y • Z correapondi111 to the color of a source having an equal­ eDergy spectrum. All x + y + z • 1, this white point appears graphica.lly at x • .33t; y • .333 and represents a position of zero purity. The outer periphery of this diagram is a locus of points of 100% purity for visible wavelengths. A line draw. from any point on tbi8 periphery to the point of equal energy (I) represents all purities between 100% and O for that dom:lnant wavelengt~. For exa111ple, a line is ahawn for a light of dominant wavelength o:., aicro•ters with the 0%, 50%, and 100% purity points indicated. An aviation green light of this dominant wavelength would have to have a purity of only 32% to •et the regulatory requirements. Aviation red, however, would require a purity of nearly 100%. The te111perature scale along the bottom of the diagram, showi.Dg a range from 1000 K to infinity, contains calibrations for source color te111peratures. Note tbat each cemperature has a calibration •rk 011 the curved line above. The curved line is called the ''Planckian locus," and represents the chro•ticitiea of blackbodies at different teaperaturea. In practical applicationa, it is accepted as representing the chromaticities of incandescent bodiea 1Ncb u lamp filaments. The numbers along thia curve 011 the CU diagr&11 indicate the color temperature in Kelvins. Cll illuminant "A" can be represented on this curve at the 2854 I. point, illuminant "B" at about SOOO K and "C" at about 6800 K. llluliinan.t A represents the spectral distribution of typical tungsten-fihment incandescent lamps, iilum~nant B represents- the spectral discributioa. of average noon sunlight, and illuminant C represents the spectral distribution of average daylight. Chap l Page 9Par l 4'1•.U O • ti •I ### Page 15 29 .July 19'7iAC 20-74 0 .I C.LE. CHROMATICITY DIAGRAM ,,,.,. '• IOUAL ClflllOY AT I CII ILLUNINANf •a•at Hl4 • ­+ . U.S. AVIATION COLOR LIMITSc1----t----t---=.::~~~~~!....:!!!!!.!.~____:i.e AVIATION tlllHII y:0.4H •• 0 + ,'YtA..WHeTe:..: c.I.E. CIIR.ClfATICll'Y DIAGRAM 11!.,.,.l:CT"IVE U AUtilJST 1971 ~PRlOr:t TO HAUCIUSTte7t Figure 1.5 Pap 10 Chap 1 Par 3 ### Page 16 AC 20-7429 .July 1971 1be color of an object depenf:is on the spectral characteristics of the illuminant as well as the nature of the object. For example, fabrics change color when moved from the light of ordinary tungsten­ filament bulbs to fluorescent light. Any accurate system of color specification must account for this fact by relating the color to a specified light source. In specifying a color that is going to be used under known conditions of illumination, the tristimulus values for the standard illuminant conforming most closely to those conditions should be used •. For example, in coloring an aviation red light cover, the color temperature of the light-source must be considered. Some red glass filters change color as their temperatures change. As the temperature increases, the light passing through some red filters becomes more red (longer wavelength) and less intense. For this reason, red-n:i"ters are generally designed tobe near the yellow limit (shortest wavelength) at room temperature. Then, if the operating glass temperature is consistently higher than room temperature, aviation red light will be produced under all operating conditions. By designing to this yellow Umit, the maximum intensity will also be obtained. Glass of other colors changes slightly with temperature, but not enough to be a problem. .. Chap 1 Page ll(and 12)Par 8 ### Page 17 29 July 1971 A~ 20-74. • CHAPTER 2 MEASUREMENT COHSIDERAnONS 4. GENERAL. The meascrement of visible radiated energy ls called photometry. Instruments for measurement of the amount of a light, regardless of their calibration, measure only flux, and care must be .taken when converting to various photometric units. An additional precaution is necessary because photosensitive devices,unless properly filtered, do not have the same characted.stics as the human eye. There are four general types of light measurements: . a. ·Luminous Intensity - 'lbe luminous flux emitted per unit solid angle in a given direction (candelas). b • Illum:b:umce - 'lbe luminous flux incident per unit area on a surface at some distance from the source (footcandles). c. LWD:1.nance - Luminous intensity per .nit projected area of surface (candelas per square foot). d. Ch.romaticity - The color quality of light determined by its chromaticity coordinates. In addition to the above light measurements, the efficiency of light covers is sometimes measured. 'lbere are two terms associated with such efficiency measurements; spectral transmittance (1) which refers to the ratio of transmitted to incident power at one wavelength or -a very narrow band of wavelengths, and l.Wllinous transmittance (T) which is the ratio of transmitted to incident total lipt power. The transmittance of a l.ight cover indicates the decrease in light due to material and color, and can be used to adjust luminous intensity values 111easured without the cover. The filtered light may be measured directly provided the photometer is equipped with filters which accurately match the lwa.inoua-efficiency function. S. INTENSITY. The instrument used to measure the luminous intensity of lights is called a photometer. Photometers can be placed in two general classes; "~ual." and "direct-reading photoelectric". a. Visual Photometers. Before the invention of photoelectric cells, most instruments for measuring intensity employed the principle of balancing two adjacent fields visually. With these photometers, a test light and a standard light of known intensity were viewed Chap 2 Page 13 Par 4 ### Page 18 AC ·zo..74 29 .July 1971 siaultaneously. By adjusting the relative distances from the viewing point, a balance was obtained, and by applying the inverse square law, the intensity of the test light coulJ be Jetermin~J. Although visual photometers have generally .beE'n supcrseJed by direct-reading photoelectric type instruments, many are still belng used. b. Direct-Reading Photoelectric Photometers. Photoelectric devic.es are now being used to detect and convert light energy to electrical energy for measurement. A photometric system for precisely measuring the magnitude and coverage of aircraft lights usually consists of the following: (1) Goniometer. This device includes. an attachment position for the light unit which can be moved around two axes of freedom. The vertical and horizontal positions are calibrated, and. in so111e cases the information is remoted to recorders so that a plot of intensity vs. direction can be made directly. A goniometer of this type is installed in the photometric labor~tory of the Nation.el Bureau of Standards in Washington, D. C. (2) Tunnel and track. A dark tunnel, including baffles to eliminate stray light, is located in line with the goniometer. A photodetector is placed on a carrier which can be moved on a track to vary the distance between the goniometer and the photodetector. Position information is usually remoted to a recorder. (3) Photodetector. Photodetectors are of several types, and read-out in units such as milliwatts, microamperes, etc. By conversion factors, footcandies (illumina.nce) can be computed from the read-out. Theu11 by means of the distance information, a calculation of intensity can be made. For steady lights, measurements are concerned with rate of flow of light entering the eye, analogous to gallons per minute into a container. For flashing lights, however, the measurements are concerned with the quantity of light per flash entering the eye, analogous to galloa.s. The quantities· are proportional to footcandles and footcandle-seconds respectively. Since the inatantaneous illuminance varies during exposure to nasb.ing lights, integration is necessary to determine the footcandle-seconds. As discussed in paragraph 2 of Chapter 1, the computation of effective intensity requires a candela-secon.cl measurement. Candela-seconds Chap 2 Page 14 Par 5 ' / I ### Page 19 29 .July 1971 AC 20-74 can be coaputed from footcaadl• Ncoada by 11<iplyiq b:, the diata.ce (:in feet) •qua.red. care ... t be taken not to overload a photodetector by too mch liaht u it caa. saturate ad ita rupoue becoae a.on 1~. Integrating photome.ters are available which electronically perform the integration an.cl read out the total exposure in 111.crocoulombs. These photometers are used only on short duration strobes where the entire flash is integrated. A 111.crocoulomb is a microampere-second, and a calibration factor ia used to c.oa.vert a llicrocoulolllb reading to footcandle-seconds. Then, IIUl.tiplyiAg by the distance squared· · gives ca:Adela-secoads corrupoa.ding. to the n.ume.rator of the equation for effective intel\Sity. Strip recorders or recording oscilloscopes are generally used for longer duration flashu, such as rotating.beacons, and •cbaa.ical ia.tegratiOD is then performed. ( :. 800 ,.. !: 600 en z w t­ 400 ~ 200 .. . - \ j ~ I -J. -l ./ " J_ I INCH ~2-t, ..... 1. f .05 SEC.- Sr:at.P IECOIDDIG or FLASB. tigu.re 2.1 Pip.re 2.1 ehowe aa. example of a recording aade by a etrip recorcler. The paper 1a IIO'led horisoa.tally at a liDear rate so that each division repreeeate approximately •05 eecoa.da • 'the recorder is calibrated so that each vertical divi.81011 represents 100 candalaa. After the fluh ia recorded. a •chanical integrator (plaaimeter) is ued to trace the recordiag and obtain the are.a. in can.dela-seconde. between the limits of t2 aa.d t1 • This area divided by 0.2 + t2 - t 1 gives tbe effective intensity. The values of t2 and by and are selected to •x:lm:Jze the computed effective ia.tel\Sity. 1n the Cbap 2 Par 2 Page lS t1 are deteral.Aed experilllentati011, ### Page 20 29 July 1971 AC 2Q- .74 example of figure 2.1 the flash has an area betwen t 2 and t1 of approximately 51 c:andela-seconds. When divided by0..3 seconds (0.2 + 0.1) the effective intensity is 170 candelas. The peak intensity of 850 candelas,therefore, has an effective intensity of only 170 candelas. A method for selecting t2 and t 1 is given in Chapt~r J. When mea:suring colored flashing lights, the pi)otodetector cannot always be relied upon to give·accurate results, even with luminous-efficiency-correction filters. The alternative is to measure the effective intensity with a clear cover, and then with a spectrophotometer. determine the relative luminous transmittances of the a,o CO\Ter& The effective intensity value measured through the clear cover is then reduced by this luminous transmittance factor.· Spectrophotometers are discussed in paragraph 3., ~· J. fQ!:.Q!• Color can be evaluated with a visual photometer by comparing a sample against a filter of known color. In such comparisons, the same, correct color temperature should be used for both sources. However, there has been increasing interest in the use of photoelectric instruments for the measurement.of chromaticity of colored lights. The following is a discussion of some of these instruments: a. Spectrophotometer. Spectrophotometers break up a self-contained light source into a spectrum by prisms or gratings~ so that narrow bands within the visible spectrum can be individually applied to a test ware (such as a light cover). Although these are not single wavelengths, they are very narrow bands approximately five nanometers wide. Determining either luminous transmittance (T), or chromaticity coordinates (x, y, and z) with a spectrophotometer involves the measurement of 40 transmittances (t), spaced 10 nanometers apart, throughout the visible·spectrum. Mathematically, these transmittances are used as follows: (7)(6)X • !:~88x.Etti>. (5) The values for x, y, and i are found in Table 1.2, and represent the relative amounts of primaries required at each. wavelength. the.E in the equations represents the spectral distribution of the light .source, and is published for certain illumfoants such as C.I.E. Source A. Tables are available which list the products 'il::, ~' and U: for certain illuminants (NBS Monograph 104). These numbers are sometimes found on a computation f'l>rm as shown in table 2 .l. If the light is not a standard source., a table 111st be developed from measurements of the energy distribution. When each of the 40 lines have. measured values fort logged, the remainder of the sheet can be filled out with data computed by hand, calculating machine, or computer. For example, assume a measured value fort at 380 nanometers of 0.078. Then iEt would be 0.078. y!T would be 0.000, an'd Ur would be 0.468. Chap 2 Page 16 Par .5 ,,,,,.,-.... ~. . ### Page 21 29 July 1971 AC 20-74 Guide for Computation of x, y, t, aad T Observer; c.1.1. Staadard 1931 Sample Basic Stiaulua: Equal Eneray llluad..a.ut: Planck 28S6 ~ cc.1.1. standard A> Wave Leqth Nanometers T iE YE iE xEt iET iET 380 o. l 0 6 390 o. 5 0 23 400 o. 19 l 93 410 o. 71 2 340 420 o. 262 8 1256 430 o. 649 27 3167 440 o. 926 61 4647 450 o. 1031 117 543S 460 o. 1019 210 S8Sl 470 o. 776 362 S116 480 o. 428 622 3636 490 0. 160 1039 2324 500 o. 2' 1792 1509 Sl0 520 o. o. .57. 42.5 3080 4771 969 sB 530 o. 12.14 6322 309 540 o. 231! 7600 162 5SO o. 3'U 8568 75 560 0. S510 9222 36 570 o. 7571 9457 21 580 0. 9'H 9221 Ii 590 o. 11579 8540 12 600 610 0. 0. 12704 12669 7547 iJ:H 10 4 620 0. 113'3 5071 5 630 o. 8980 3704 640 o. 65Si 2562 650 o. 4336 1637 660 o. 2Hi 972 670 o. 144i 530 680 o. 804 292 690 o. 404 1ii 700 0. 201 75 710 720 0. o. llO,, 40 19 730 o. 28 10 740 o. 14 6 750 o. -6· 2 160 a. 4 2 710 o. 2 SUMS 109828 100000 3SS47 X• Y• z.. y x•ii,"y.i:z' ~i+t+i' z• --.X+Y+Z X z :z: 1 and zx1 CX>HPUTATJON FOBM Table 2.1 Chap 2 Par 6 Page 17 ### Page 22 29 July 1971AC 20-74 r'' . Su11111ing the column for xEt would yield X which is tht! relative . i, amount of red primary required for the match. Y and Z can b~ found.with the othe.r two columns. Then, the chroa.iticity coordinates for representing the sample on a chromaticity diagram. or evaluation against regulatory requirements is f,,und as follows: X"' X y. y z = z X+Y+Z X+Y+Z X+Y+Z The luminous transmittance T of the ware can be found from the same computation sheet as follows: n1e sum (Y) is divided by the sum of the yE colwnn. of the 9Et column This is possible because y and V(A) values(lumioous-efficiencies)are identical. For example, if the sum of the yEt column is 24407, dividing by 100,000 gives .24407 or 24.4%. The values given in this cable have been adjusted so that the sum of the yE column is a pOW'~r · of ten to simplify computations. This means that only 24.4~ of the'light incident on the ware is being transmitted through it. A more detailed explanation is given in the Appendix as "Tristimulus Colorimetry and Aviation Lights." b. Spectroradiometer. Spectroradiometers are similar to spectro­ photometers, but cau be used to measure the spectral distribution of external sources over the visible spectrum. a wider ran2e of wavelengths than just c. Brightness Meters. When evaluating the color of ware with these instruments, a standard filter is used for comparison. The results are not chromaticity coordinates (x, y, and z), but are in or out of tolerance indications. Such procedures, due to filter limitations. are used only on highly saturated red glass (sharp cut-off). One method of determining whether a color 111eets a specific requirement,by using a brightness meter and a NBS filter, is given in MIL-L-25467C. The filter specified in this procedure has a yellow limit corresponding to instrument and panel lighting red (Nation.al Bureau of Standards Filter No. 321S). However, the procedure has been. used with an aviation red filter (NBS Fil,ter No. 3647A). Th.e procedure is a Go/No-Go measurement with the NBS filter used as a measurement standard. A brightness reading is taken of a colored aviation light at 10 ft. distance.. A second reading is taken after a NBS filter is added in the light path. The ratio of these 2 readings m.ust approximate a similar ratio obtained using a white light source in place of the colored aviation light. In the second case, a first reading is made with Chap 2Page 18 Par 6 •.:··· ### Page 23 A.C 20-7429 July 1971 one NBS filter and tbe second reading is made with two NBS filten. In this way, the aviatioa. light color is compared to the NBS filter color. The two ratios must not differ over 3% (in the yellow direction) to qualify the test light color. d. Tristimulus Colorimeters. If the response of three photocells could be adjusted by glass filters, so their responses follow the curves of the c.1.E. Standard Observer,i, y, and i (see Figure 1.4), they could be made to yield direct measurements of tristimulus values X, Y, and z. Complete success of these colorimeters depends on the ability to duplicate the C.I.E. Standard Observer System. Acceptable instruments Cl)Uld simplify the measurements and reduce the required data processing. Presently, such instruments have more application to production line measurements than for showing initial compliance. 7. TEMPERATURE EFFECTS. All glass filtering elements have their color and transmittance affected in varying degrees by increased temperature. The change is more pronounced for red than for other colors. One manufacturer of glass baa pu.bli1bed data such that different red glasses are identified by their percent transmittance at room temperature. For example, red glasses are identified as 12.6%, 25.3%, etc~at 78° F. For each number, the color and transmittance at any temperature up to 500° Fis charted and plotted. Most red glass colors are reversible up to the softening temperature(over 800°F). Reversibility means that after beating, when the temperature i8 returned to 78° F, the original color will return. Glasses that have transmittances of 25% or more at 1s• F have trans­ mittance vs temperature curves which are essentially linear up to 300° F, and transmittac:.es chanae approximately 0.5% for each 10° F change in temperature. In application of these filters, proper evaluation of their color characteriatic at elevated temperatures requires knowing the following: a. The initial glue temperature, color and trans111ission. b. The range of glass temperatures found in operation. c. The type glaH used in the filter and its characteriatics. Generally, an increase in r~d glass temperature makes its color more red and decreases ua translliesion. The amount of such changes is determined by the temperature range of the glass in operation and the charac­ teristics of the alaaa. Chap 2 Page 19(.nd 20) Par 6 ### Page 24 AC 20-7429 July 1971 CHAPTER 3 **MEASUREMENT DATA** 8. GENERAL. Aircraft exterior lights.,on which measurements are required, include position and anticollision lights. Measurements include intensity (coverage and overlap) and color. a. Position Lights. The airworthiness requirements for aircraft position lights are given in FAR 23.1385 through 23.1397, FAlt 2S.1385 through 2S.1397, FAlt 27.1385 through 27.1397 and FAlt 29.1385 through 29.1397. (1) Intensities. (a) Horizontal Coverage. Figure 3.1 shows the minimum intensity requiremea.ts for the horizontal plane at 0° vertical. Overlap limits are not shOW'D. as they vary when inteasities exceed 100 candelas • · (b) Vertical Coverage. Figure 3.2 shows the minimum intensities for any vertical plane. The value of "I" indicates the maxillum required candelas for a given horizontal position. (2) Color. A graphical presentation of the chromaticity coordinate limits for aviation red (left). aviation green (right), and aviation white (rear),is shown in figure 1.5. b. Anticollision Lights. The airworthiness requirements for aircraft anticollision lights are given in FARs 23.1401, 25 .1401,. 27 .1401 and 29.1401. Cl) Intensity & Coverage: Figure 3.3. (2) Color: Each anticollision light llll&t be either aviation red or 'iv'rition white. t. POSITION LIGl:I.T DA.TA. a. Intensity. Measurement of position light intensity requires photometric equipment such as that described in Chapter 2,paragraph 2. Figure 3.4 and 3.5 show typical recordings as·made in a_photometric laboratory. 'lb• data elaould include enough diatribution plots to ade1:1._uately eubatan.tiate coverage. The following data should be. sufficient": Forward Bad and Green Position Lights. A horizontal distribution curve in the zero degree vertical plane from directly forward outboard through 110 degrees (fiaure 3.4). Vertical distribution curves fr011 90 degreea up to 90 degrees down at O, 10, 20~ and 110 degree horizontal points (figure 3.5). In addition to these distribution Chap 3 Page 21Par 8 ### Page 25 /,.,,... ........ AC 20-74 29 .July l97l • urvl!s, a visual lnspe,;tion through tht! enli re nn•41 shm1hl ht• llld•le to determine whether or not there are any not I\'.c.ih le 1:1lrnd,1ws or areas wh~re visual observation would lttd-h':Ht! •j11cstionc1blc conform.m,:e. lf any sud, 11uesti11nnhl\! an•.:1s ,II',' uotu,l. turther aHrnsurements should be made in those arna::; t,, Jeaaoni:.l1,1te satisfa,:tory coverage. II"-!'" ~!..!'l l'.!!~_i_tion l.igl~.'· :\ horizonr,d distrihution from 70 dl.!grt!es right t,> 70 rlti!!gri:t.?s left , .. · dir.?ctly to thl.! n,•.1r. Three vertf,:al dhlri.butlon , urve.: ::rom 90 degrees up to 9:1 ,l~greus Jown through the fol luwlng horizontal points: dir,•N ly .,::.tcri\, 70 ,lugn!e~ lut'l of di r\.!ctl·1 to the ri?ar, J.nd /0 dl~gr·..ics n~ht of dir~ctly to the rear. Laboratory reports of such awasurem.t:nts should ,,lso ln1. lude at h!aSt the followiug: (11 A li1:1t of the test equipment and calibration dates for light ~tandards which should show calibration against the lab working standard within the past JO days, and thu working standard against the lab primary standard within the last J80 d~ys. The laborat9.ry primary standard should be traceable to the Nntional Bureau of Standards. (2) If~ luminous~(ficiency-corrcction filter is included, data adjustment for filter errors should ba shown and substantiated. (3) Ii transmittance measurc111ents aru used, the data should show ~1Jjustment for the comparison in transmittance between any r: lt?ar filter useJ during the intensity measurements and the transmittance of the colored filter. If a clear cover is us\i!d, it should have the identical shape as the colored cover. Transmittance data should be shO\oln on a computation sheet such as shown in Table 2.1. Also. if a spectrophotometer is used it should be substantiated that the sample used in the ~asurements is representative of the actual light cover. (4) \~1en red glass is used, the data should show the temperature ,,f 1ight covers during measurements and data on the transmittance characteristics relative to temperature. Measured intensity values $hould be adjusted as follows: (a) For measurements made with the red cover in place, adjust the intensity values to those corresponding to an ambient temperature of 100°P. If no actual measurement is made with an ambient temperature of 100°F, extrapolation should be supported by data. (b) When transmittance data i~ used, values should be adjusted to correspond to a glass temperature equivalent to that of the outside surface of the light cover. Glass temperature measurements should be made after the glass has stabilized with an ambient temperature of at least 100°F. Optionally, a temperature of 130°F should be allowed in lieu of measured temperature. Chap J Par~ ### Page 26 29 J'uly 1971 AC .ZlJ-74 (S) A description of the procedure used to obtain intensity and transaqttance data, including the calculations. A diagram of the test set-up is desirable. This description and diagram should show: (a) Intensity measurements made from a distance sufficient to give accurate results with the linear operating range of the photocell of prime consideration. The distance should always be at least 10 times the diameter of the light source and preferably greater. (See IES LiRhtinR Handbook, 4th Edition, page 4-18) (b) Voltage measurements made as near the light source as possible, using a suitable meter when considering accuracy and loading. Current readings should also be recorded and data supplied to show where the lamp falls with respect to the manufacturing tolerance limits. b. ~- Position :tight color measurements :require equipment such as described in Chapter 2, paragraph 3•. Aviation green conformance should be showo. with data in chromaticity-coordinate form (x, y, and z). Aviation red conformance should be shown by the same type data, or by the optional brightness meter and filter method. When spectrophotometric procedures are used, the data should include a computation sheet such as shown in Table 2.1. Laboratory reports which accompany the data should include at least the following; (1) A list of the test equipment with, when applicable, calibration dates. ' (2) When red glass is used,' the data should include the temperatur~ of light covers during color measurements, and data on the color characteristics relative to temperature. Red glass data should also include the following: (a) For measurements made with the red cover in place, substantiating data to show that the color will be within limits when the outside temperature of ~he glass 18 78•F. (b) If chromaticity-coordinate measurements are made, measured values should be adjusted to those corresponding to an outside cover glass temperature of 78°F. (3) A description of the ~rocedure used to obtain the color data. A diagTam of the test set-up is desirable. Chap 3 Page 23 Par 9 ### Page 27 AC 20-74 29 July 1971 3. ANTICOLLlSION LIGHT DATA. a. Intensity. Measurements for "effect"ive intensity" require techniques as described in Chapter 2. paragraph 2.b.O). The light may be measured as a white light, and the intensity values adjusted according to the tran,.;mitlance of thi, red cover. The comput3tion slu~et used to determine the chromaticity-l·oordinates contains the data for determining the luminous transmittance of the red cover. lf a clear cover is ust!d in the intensity measurements. the ratio of the transmittances ~r the tw~ cuvers -• bt:! used to correct the data. ·ro shaw fi"' lJ of covf'ra~t!, d r:ombinilt. ion of vertical and horizontal measureme1Hs is lh,!~~:,sary. Figure J.6 is a typical pr~sentation <.>f verti.cal et fectivc intensity dist rihution and is shown with the FAA minimum intensity requirements. Such l'urves are constructe iW ! : :H! ;;;1 :l iiil Uil ;!i: 1m ,::; ;;:! 1·:;; '.::· :f; i!:: :ff: ;J:j :!"1• :l;j !!!i :!:: ;i); Ii:! rjj l!i: : i'Jjii It:;;,: . t'I •jll !Iii j,:i jl•, ;;i: ;! • 1'.I: !::: ;: ::j! !'Ji q:: jj:: !-! •••• •, ,•·• •••• ,. , ··' •••• ,, 1 ti,,•••••··••·•, ·••• • .t : IJ .:.•n' ::,!; l •.:: :, ·:; ?!: ;',! Ii: J, •: Ut: !t U,! n. :.:: .:~ ......,. j' . l'!J , •. 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Ht ti1 llh tit: t±:: :,:: ~'!::! !iP 1m I! 1111 ![!il nii u ,., . ltr -~rt~ ~ ........ t .... • 1tl . i. 1204' 100• 80"' -w 40• 2.0" 0- 20• 40"' TYPICAL HORIZONTAL INTENSITY DISTRIBUTION- POSITION LIGHT FIGURE 3.4 Chap 3 Page 30 Par 10 ### Page 34 29 .July 1971 AC 20-74 =='= /: :: ·1= :: : ::·· ·' - ::: ·:.:.: ::~. .:..::.' .. :: ~· .. : : ;: .·~; ·~ ....... . .. . . . .... :-.· :-- :.,· :_: ·:.:: ·I. ~E- =t ). t= > 1:""' ::::,.. :·:: ::,: ·:.: :: .. ::·: ,:. ... · ,:.;.;.+:-~.:.+-:-;.+-;.;.;+-;~""+-,-+-----1....:i~1:=:1,-+,,.;;--.,...-1-,--.. :·:· ...... :::·: :.-~~-­ ·:: :·:l .... , ·;.; ;:·· ....... ·. ,.. ····-!­· i · ···· · · :"·i· ·,., · l ~ I f"' 011 ~· . • l : . I . . . . --· -t·. -+· ·--·-·. i - __.j__ --~ .1 .:... -!-- .... ; ...•.. ·+··.. ; . · i .. +·· I ": -! ..... i l i I i : i .. t : L! I" : i ! . 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I· : : .\+· . +--t-·~,·...':_'_·1::_ .','-. ,.... --=-.·.....: : ... ::...,·: -.J_-:T-.:....·-. : .:.. . 80'" 60" 40" 20" O" - 20• • 40• • 60" -80'" TYPICAL VERTICAL INTENSITY DISTRIBUTION- POSITION LIGHT FIGURE 3.5 Chap 3 Par 10 Page 31 ### Page 35 200 29 July 1971AC 20 ·74 **ROTATING BEACON** **EFFECTIVE INTENSITY DISTRIBUTION** 28.0 VOLTS I • 67 AMPERES 50RPM AVIATION RED LENS 17S 150 125 75 ) ) C 'If / I l ~ I 81 ) . I I **MINIMUM** INTENSITY REQUIREM~NTS I \ V j I \ I ' I'\ ·""' . "" "' Fl GU RE 3.6 so 25 0 -100 +100 +200 +300-300 "' DEGREES VERTICAL << :. 3Chap 3 Page 32 Par 10 ### Page 36 **EXAMPLES OF TYPICAL TIME-INTENSITY CURVES** SHOWING EFFECTIVE INTENSITY CALCULATIONS SECONDS PER INCH= .0666 CANDELAS PER INCH= 200 THIS CURVE TAKEN AT -5° ELEYAJIQN ( 8 > = TO **ESTIMATE LINE IS CLOSE ENOUGH TO 141 FOR** PRACTICAL CONSIDERATION i, ;/ ~- -··· I1200 1000 800 !c( m._600C z ,c( u 400 200 __)... ... AREA BETWEEN LIMITS t1 AND l? =3.50 SQ. I N, t2-t1 .·=l.0561N, I I 3.50 X 200 X .0666 I 173• (1,i6 X .0666)t .2 I 173 X 1.12 (HEAT CORRECTION FACTOR) 194 CANDELAS ESTIMATE LINE Is 173 FOR PRACTI CAL ~ CLOSE ENOUGH CONSIDERATIOt __j~V •-·- -·- \ 1.056"-- '---- --- >n ,~ ..,r .i:-· ,0703 SEC,t1 ½ I . ,THIS CURVE TAKEN AT 00 ELEVATION (A) 1200 1000 800 600 400 200 _/ t, **AREA BETWEEN LIMITS** t.1 ANDt2= 2.90SO. IN. t.2 - t1 =1,109 IN. I I2. 90 X 200 X • 0666 ., 141I (1.109X .0666)+.2 I l 141 X 1.12 (HEAT CORRECTION FACTOR)= 158 CANDELAS I ,/1I --1.109 11 ..... '-.....---1 1'0666 SEC. I,0739 SEC. t2 • .., 5 C "' ~ .w ...., ### Page 37 AC 20-74 29 July 1971 . I I I I I EXAMFU OF TYPICAL EFFECTIVE INTENSITY CALCULATION T . I I ' . ED ON I AX AREA IN SQ. IN. X sec. PER IN. X CANDELAS PER IN.BAS eM • "" , • I (t2 - t, IN INCHES X SECONDS PER IN.)+ .2 I I Iill ESTIMATE !gl SEC. PER IN ... •0666 I I AREA BETWEEN LIMITS t1a and~= 9.0 SQ •• IN. DISTANCE FROM t.1a TO t.201= 7.04 IN. I I 9·00 )$ ,0666 X 20 • 17.9 CANDELAS (7 .04 X .0666) +,2 I2NO ESTIMATE (bl I SEC PER IN . = • 0666 ! I I AREA BETWEEN LIMITS t1b and tit>• 4.60 SQ. IN. I I ' IDISTANCE FROM t1b TO t,j:, = 2.165 IN. I I . I4.60 Xt'0666 X 20 I .. 17.8 CANDELAS (2.165 X .0666) +.2 i l!P ESTIMATE.fsl I I SEC. ~ER IN. = ·1"6" AREA BETWEEN LIMITS t.1c: ANO l2C = 7.13 SQ, IN, I I , DISTANCE FROM. t.1c: TO 12<=-t-= 4,765 IN. I , 4,60 X, .0666 X 20 = 18.4 CANDELAS (4,765 X ,0666) +.2 I I I 18,4 X 1.12 (HEAT CORRECTION FACTORl.:=. 20.6 CANDE~S 80 I I f ~ THIS CURVE TAKEN AT I . -2rf' ELEVATION (c:) VI ° 8.8 10 .88 110.0 **TYPICAL FLASHTUBE MEASUREMENT DATA SHEET.** Fiere 3.9 Chap 3 Page 35(and 36)Par 10 ### Page 39 l 29 July 1971 AC 20-74 AppenJix APPENDIX 1 **GLOSSARY OF TERMS** 1. CANDELA - Unit of intensity. Produces one lumen per unit solid angle (steradian). At a distance of one foot, one candela produces an illumin.ance of one footcandle. 2. CIIROMATICITY - The color quality of light determined by its chromaticity coordinates. 3. COLORIMETRY - A method for measuring colors and specifying them in numerical or definite symbolic terms. 4. COLOR TEMPERAnJRE - The temperature at which a blackbody must be operated to give the same color as the source, usually expressed in Kelvins (K) • 5. DOMINANT WAVELENGTH - That wavelength of spectrum light which,. when combined with neutral light in suitable proportions.matches the color. Neutral light is light for which the cbromaticity coordinates are x • .333 aud y • .333. 6. EXPOSURE - The product of the illumiDance and the time during which the material is exposed to this illumin.ance,.or E •it.The unit of measure is the footcandle-second, which represents an exposure of l second to a source having a light intensity of 1 candela at a distance of l foot. 7. !!!!, - The attribute of color determined primarily by the wavelength · of light entering the eye. 8. ILLUMINANCE - The areal density of luminous flux incident on a surface, iD lumene per unit area or footcandles. 9. INTENSIT'f - Flux per. unit solid angle from a point source measured in lume:na per ateradian or in candelas; often called candlepower. 10. 1!Q!!! - Radiant energy that produces visual sensations. 11. LUMEN - Unit of luminous (visible) flux. Luminous energy emitted ~econd by a uniform point source of one candela intensity through a solid angle of one steradian. 12. UJMIN.AHCE - Luminous intensity of a surface iD a given direction per unit of projected area of the surface as viewed from that direction; measured in candelas per unit area. page 1 Par 1 ### Page 40 29 July L971AC 20-74 Appendix 1 13. LUMINOUS FLtJX - The ti-me rate of flow of light, sometimes called light power. 14. PHOTOMETER- An optical device that utilizes equations of brightness or flux to permit the measurement of a photometric quantity, such as intensity, illuminance or brightness. 15. PUOTOMETilY - The measurement of visible radiation on the basis of its effect upon the eye under standard conditions. Visual photometry involves the adjustment of two parts of the visual field, in order to identify or to determine a minimal difference. Photoelectric photometry involves the measurement of the flux incident on a receiver from a test and a standard source at known distances. 16. SATURATION - The extent to which a chromatic color differs from. grey of the same brightness, measured on an arbitrary scale from 0% to 100% (where grey is 0%). Also called "purity". ~ 17. SPECTROPHOTOMETER - An instrument designed to measure the· spectral . transmittance or reflectance of objects. Used primarily for comparing, at each wavelength, the flux leaving the object with the flux incident upon it. It usually has a built-in light source. 18. SPECTRORADIOHETER - An instrument used to measure the spectral distribution of radiant energy. 19. SPECTRAL LUMINOUS EFFICIENCY V(A) - Quotient of the luminous flux at ·a given wavelength by the radiant flux at that wavelength normalized by dividing by the maximum value of that quotient, formally called luminosity factor. 20. STERADIAN - The unit solid angle. That solid angle originating at the center of a sphere which subtends an area on the surface of that sphere equal to the square of its sphere radius. A sphere contains 4ff steradians (see Figure 1.3). Par 13Page 2 ### Page 41 gUANTlTY SYMBOL DESCRIPTION Flux Rate cif Flow of Light ~ Point Source Uaht PowerIIntensity Concentration of Intensity fro111 surface source (brightneaa) LLuminance Surface Received Light l>ensity EIlluminance " Distance Traveled DuringWavelength a Cycle Two Dimension AngleswSolid Angle Electrical Energy Rate V (A) Eye Response to varying wPo11er Luminous Wavelengths (Table 1,1)Efficiency UNIT -1u111en Candela footlambert lambert footcandle meter steradian watt EQll\'ALENT 1 lumen/steradian (1/,) canddas/tt­ 1 /" r,2 ,. __ ,,,_,1, ••. It ...2 l lumen/cm2 2.054 candelas!in2 l lumentf1.2 R~tio of velocity=~ frequency of radiation Total Solid Andes/411 (Sphere) jouleslS1t.: y ~ lumens • watts x bllU X V{•,I :andelas • fo-,t.:andld x dlstlnc~ squared h·,•tcandles • car,d.elas~Hatan.:e squared ::ictt:r • 106 mlcromeu,rs (,.a) • 109 nanom.!ters (nm) • 1010 ang~cro!'!\lo (A~, steradians• surf.ac.E: arta/ dlstanc:E: 11uar•: ### Page 42 AC 20 .. 7429 July 1971 Appendix 3 APPENDIX 3 TRI STIMULUS COLORIM~:TRY ANO AV IAThlN t.ll~IITS Althou~h the energy distribution ot a colored 1.i.~ht may t.·xtend tlu·,,u~lh•11t the visible spectrum, the d1arat:terisLics ot: vision are sui:h th,:tt a combination of three prim.ary colors can match the li~ht t,, tht! satisiact i,,n of the eye. The apparent matc:.h of two colors of differ~nt spectral con.t~nt is called "metamerism," and the two colors are called a 11 metameric pair. 11 This method of matching or rt!producing a color is the basis for tristimulus colorimetry. The tristimulus method.is tu measure the energy distributi"n and then to convert thi1::1 information i.ut,) the tristimulus values which form a metameric match. Figure 1.4 of thii:. ,'.ir,:ular shows how to mix th~· three CIE primary colors in order to match any w,1ve Itmgth. tf we have entergy distribution throughout the visiblt! sp~,·tnan, we simply mul.tiply the rela:fri? pt,wer amplitude at aach wavelength ti\' thl' •·vrresponding tristimulus value!:. i. y, and i for that wav~length. 'Jlh:11, by adding up all the measurements a total amount for each of the pr ima1· i~:-. i.s found. Mixing these amounts of X (red), Y (green), and Z (blue), wti ac,:omplished a metameric match. Thus, X • i:~ig Ex Ii.A where E i~ the power, and i is the proportion of red primary required for that wavelength; Y and Z are found similarly. tn this way, we can dt!termine the required amounts of primaries to match the color of a source or in the case of lights, the lamp. C.I.E. standard illuminant 0 A" (incandescent) has a published power distribution, as have several other sources, and tables of Ex, Ey, and Ez are available. If the source is non-standard, the E values must be measured, and by computation, the tables developed. The significance of this information is that the color of the light transmitted by the filter depends not only on the filter but also on the spectral distribution of the light incident on it. After tabled values for Ei, etc., are developed, they must be modified by the filter effect. Usually, this is done by measuring the filters' transmittances throughout the visible spectrum~ This gives a new colUIIIO labeled "T". Then, to obtain the X, Y, and Z required to form a match of the overall system, we must combine the data. Combining the source and filter data we solve the equations: 770 X • t380 Ex TAA etc. Mechanically this is done as follows: 1. Measure the power distribution of the light source {E) in 10 nanometer steps from 380 to 770 nanometers (40 measurements). ### Page 43 --- 29 July 1971AC 10•74 Appendix 3 2. For each step, combine (by multiplication) i, y, and z information from tabled values to obtain Ex, Ey, and Ez (40 values). 3. Measure the transmittance (r) of the filter at these same 40 points. C01UbJne these numbers wlth previously computed values to obtain 40 values tor Elt, Eyt, Ezt. 4.· Add the 40 values for Ext to obtain X; the amount of red primary required for a match. Repeat for Eyt and Ezt to obtain Y and Z. 5. Compute x • X • y • Y , and z • Z This X+Y+Z X+Y+Z X+Y+Z gives the d1romatkity t.:nonl in.:ttPs which will form a metameric match of the light color. The transmittance of a light filter' is,by definition, the ratio of transmitted to incident light power. The transmittances (T) measured at the 40 sample points do not consider eye response, nor the power distribution of the illuminant. Therefore, when we evaluate a filter for overall transmittance,we :11Jst combine the following data: L. distribution of. source . . . . . . • E 2. !::ye response luminous-efficiency function • • • y [y was adjusted to correspond to V(A)) "3. Filter transmittance distribution … t These three variables were combined when developing Y as r~~g Ey ,A).. As this is also a measurement of visible transmitted light magnitude, dividing by the incident light will give the transmittance of the filter. The incident light is the same as the transmitted ligh5 of we omit the filter transmittances. Therefore,the incident light is t 3~0 F.y AA and the transmittance T • • ·r;~ Ey T6A r~i8 Ey A). Page 2 . ### Page 44 /C lU-1429 ·July 1971 Append1.x 4 APJllo:Nf>lX 4 **BIBLIOGRAPHY** 1. l:i.sion in Milllary Avfotion - w,ur: Tt!•·hnica l Report 58-J99, ASTIA D,,1.,;um~nt Nu. AO 207780. 2. l:'ca11damental:, c,f LighL JnJ Lightf111; - ,;,int!nll t::lec.:tric Company. Large l.i&lllp Ot.:partmerrt, Clevc.:Jaud, Oh'fu. 3. a-",~der.tl Stat1d:Jrd No. j, with ,\itlendllliCnL l, March 21. 1951. Superintendenr of Documents, Washington, D. c. 2040.2. :.. Mil-C-25050A(ASG) December 2, l'l63 - Colors, Aeconautkal Lights and Lighting Equipment, General Requirement$ For. 5. Color and Transmi:1sion Properties of Sharp Cut-Off Glass Filters .it Elevated Temperatures - c. E. Leberknight and G. E. Stone, Kopp Glass, Inc., Swissvale, Pena.sylvania, April 1955. 6. Spec1Ucat1on for Photo111etrtc Te&L Procedure, Specification CAA-110,,, June 10, 1957, Department of Cpmmerce, Civil Aeronautics Administration, Office of the Air Navigation Facilities, Plant Engineering Division, Washington, D. C. 20402. 7. A Short Course in Photoiwtry, Leu Leva., Consulting Physicist, New Yo~k. N~w York, ~lectronics Products, F~bruary 1965. 8. Collision Avo.idanc~ and Aircraft Lighting, Grimes Manufacturing Co., Urbana, Ohio, 196S. 9. Measurement of the t::ff~ccive Candlepow~r of Flashing Beacons - Charles A. Steinberger anu Marshal F. Rowland, Grimes Manufacturing Co., Urbana, Obiu, !965. 10. Illuminating Engineering Society Lighting Handbook, Fourth Edition. 11. Il!uminatin& tngineering Society Guide for Calculating the Effective Intensity of Flashing Lights, Illumination Engineering, 59 747 (1964). 12. Photometry of Colored Lights - A. c. Wall, Illuminating Engineering, 1967. 13. MIL-L-2S467C Lighting, Integral, Aircraft Instrument, General Specification For, (Dec.1963). 14. Colors of Signal Lights, NBS Monograph 7S, (1967). Superintendent of Documents, Washington, D. C. 20402. 15. U. s. Standard for Colors of Signal Lights, (1964). ### Page 45 AC 20-74 29 July 1971 Append!x 4 16. 1968 NlllDf Technical Publications. Row to Measure Light - P.B. Lape and I>. V. llyer, International Light, Inc., Newburyport, MaH. 17. Illumination Engineering• Warren B. Boast, 1953. 18. Colorimetry. NBS Mo'ftOgraph 104, 1968. Superintendent of Documents, Washington, D. C. 20402. 19. Light and Color Measurement, of S•ll Light Sources, Bode Mede, General Electric S•ll Lamp Division, Hela Park, Hew York. 20. The Measurement of the Color of Light Paitt~d by Signal Devices, by Stewart Seaae and Paul M. Fisher, Rohm and Baas Color Laboratory, Available•• a reprint from ..Color Bnaiile!trina," Reprint Dept., 18 John Street, Nev York, Nev York 10038. 21. lhe Application of a Color-Correction Factor in the Photometry of Colored Signal Lights by George K. c. Hardesty and T. o. Twiet, Naval Ship Research and Development Laboratory, Almapolia, Maryland (Technical Rote ELECtAB 12S/l;8 of May 1968) . 22. Maxilaum Luminoua Efficiency Contour Chart• for Colored Materials by George It. c. Hardesty, a. L. Booker, and J. '1'. Mctane, Nav,1 Ship l.eeearch and Develc,pant Laboratory, Almapolia, Maryland 21402 (Technical Rote, BLECLU 200/68 of October 1968). 23. Photom1try, w. T. Walsh Conatable, Third lditlon, 19S8. 24. Th• Role of Exterior Lights in Mid•Air Collielon Prevention, 'l'.B. Projector, Applied P17cbology Corp., July 1962, ASTIA·Document AD 602421. 2S. Computation of the Effective lntenait:y of na1hlng Lights, C. A. Douglaa, Illumination Engineering. Vol. S2, page 641, December 1957. --- From OpenAirDocs.org, an independent open copy of FAA data. Only the Federal Register edition on govinfo.gov is the official legal text of an AD.