Aircraft Position and Anticollision Light Measurements

AC 20-74 29 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 21 Par 8 29 .July l97l AC 20-74 /,.,,... ........

• 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 1 ight 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 Page 22 Par~ AC .ZlJ-74 29 J'uly 1971 A description of the procedure used to obtain intensity and (S) 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 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<d from points representing separat~ t?ft'ective intensity measurements.

_To· assure suffici,mt points to ,1,:.;urntely draw the vertical distribu tion curve, mcasurem.;ints are us111.ll}' made at vertical angles of :t30°, :t20°;, j:_10°, :!:.5'' and o. 'l'bree of nine such points are shown in Figure 3.6. To obtain the values for the three points, individual intensity vs time curves are recorded and processed. The processing for long duration type lights can be done from a paper recording, using a planimeter for area measurements. Horizontal coverage must also be substantiated. As the curve of Figure 3.6 r~presents a single horizontal direction, there should be enough measuTements to assure complete field of coverage. In other words, it should be substantiated th.it any variations in vertical patterns around the light will not result in an out of tolerance condition at any horizontal position.

When using the Blondel-Iley equation, the maximum val~e of effective intensity is obtained when t2 and t are chosen so that the effective intensity is equal to the instantaneous intensity at t2 and t1. To compute the highest possible effective intensity value for a given curve, estimates should be made until the proper values for t2 and t1 have been ~ determined. When the instantaneous intensity at the t and t1 points approximate the effective intensity value computed from the Blondel-Rey equation, the maximum computed value has been found. Figures-3.7 and 3.8 haw examples of data and include the mechanics for determining maximum computable intensity for points A, B, and C of Figure 3.6. The heat correction factors used in Figures 3.7 and 3.8 are used because the light cover is at a higher temperature in the laboratory than in actual operation. For rotating beacon measurements, the motor is stopped and the light is concentrated on a particular area of th~ glass. As mentioned before. red glass decreases in transmittance with heat.

Chap 3 Page 24 Par 10 AC ?0-74 29 .July 1971 For short ti• flashes such as those produced by flashtube unite, an integrattng type photometer is generally used.

1'heee iutrumnte integrate the wole flash rather than between specific limits. If an integrating photometer is ueed, the •nufacturers' calibration and operation procedures should be follOW1:Jd. For typical flashtube measurements, the value of - tl ie negligible compared to 0.2 seconds. t Computed effect ve intensity for these lights is therefore maxilillua when the entire flash is included. Effective intensity for short time fluhee can be found by the following relation: ?ootcandle-1econd1 (meter reading} x distance squared+ 0.2 seconds To improve the accuracy, several flashes are integrated and an average 18 taken. Figure 3. 9 is an example of typical flashcube meaeurement data. Information furnished usually includes the charge voltage, flash capacity, electrical energy stored (watt-sec), flash rate, and the plane of measurement.

In the example, the 15.6 watt-seconds results from the equation: ..

Energy• 1/2 s c = 1/2 (420)2 c11nc10· }

The 15.6 watt-seconds of electrical energy is partially converted to light energy. If reflectors and gas conversion efficiency are considered, the watt-second number can be used to estimate possible candelas. The test distance is given so that the meter reading is convertible to candelas. The multiplier (12S) in the example results from o /0.2. In the tabled data, therefore, the single flash footcandle·second reading times 12S give, effective intensity.

_Laboratory reports of such measurements should include at least the following: (1) A list of test equipment and calibration dates as discussed in paragraph 2.a.(l).

(2) Luminous-efficiency-correction filter data as discussed in paragraph 2.a.(2).

(3) Transm.ittaru:e data as discussed in paragraph 2.a.(3).

(4) Temperature corrections as discussed in paragraph 2.a.(4). If a heat correction factor is used, it should be substantiated by data.

(5) Procedure information as discussed in paragraph 2.a.(S).

For anticollision lights, this information should also include the •t.hod used to determine "effective intensity."

Chap 3 Par 10 Page 25 __ ,O•fl•J 2CJ July·· l 97 ~ AC 20-74 (6) For strobe sources, the spectral distribution data used in transmittance computations should be substantiated by data showing apectroradiometer mt,.tsurement.s, or pub 1 isht!d data which can be shown Le, be 3PI' I i cab le.

h. Color. Th~ me..i:;ure~nL fur c:ulot· ,,r an anticoll is ion llght

red ,·over is usuallv mad,? with a H!lectrophotometer. In thi,s measurement, thl.! ca:nputat.ion :;heel (Table 2.1) should c:nntain values for spectral ditllrihur·iou whir.la are representative of the light sourcl:! being u:~e•f. Pre··i:omputed values for ex. Ey.

and Ei are avJ.f labl" fo1 many typ~ sour,'llS and are id1ml ified by color temperature. NBS Mon<,gr.i,,h 104 has several d.&mples.

The .,;olor tempcrJ.ture and lite val111~i:; fu1· 1-:i, Ey, aud I:z must be accurately known if the 1:cs11lt:. a1:e lo be dependable.

' Labor;,1,t.ory reports which accompany tht! data should show c1t least th~ following: (1) A. list of the t~st equipment with, when appli~able, calibration dates.

(2) Temperature data as diic::uased in paragraph 2. b. (2).

(3) Procedur~ information as discussed in paragraph 2.b.(3).

Chap 3 Page 26 Par 10 AC-20•7/t 29 .July 1971

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80'" 60" 40" 20" O" - 20• • 40• • 60" -80'" TYPICAL VERTICAL INTENSITY DISTRIBUTION- POSITION LIGHT FIGURE 3.5 Chap 3 Page 31 Par 10 29 July 1971 AC 20 ·74 ROTATING BEACON EFFECTIVE INTENSITY DISTRIBUTION 50RPM 28.0 VOLTS I• 67 AMPERES AVIATION RED LENS

~

l

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MINIMUM INTENSITY REQUIREM~NTS

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DEGREES VERTICAL << :. 3 Chap 3 Page 32 Par 10 EXAMPLES OF TYPICAL TIME-INTENSITY CURVES SHOWING EFFECTIVE INTENSITY CALCULATIONS SECONDS PER INCH= .0666 CANDELAS PER INCH= 200 . ,THIS CURVE TAKEN AT 00 ELEVATION (A) THIS CURVE TAKEN AT -5° ELEYAJIQN ( 8 > I 1200 ...

AREA BETWEEN LIMITS AREA BETWEEN LIMITS t.1 ANDt2= 2.90SO. IN.

t1 AND l? = 3.50 SQ. I N, = 1,109 IN.

t.2 - t1 t2-t1 .·=l.0561N, I I I

I 2. 90 X 200 X • 0666

3.50 X 200 X .0666 1000

I

., 141 I • (1.109X .0666)+.2

(1,i6 X .0666)t .2 I

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.., 173 X 1.12 (HEAT 141 X 1.12 (HEAT CORRECTION = CORRECTION FACTOR) FACTOR)= 158 CANDELAS C ~ 194 CANDELAS

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ED ON I AX AREA IN SQ. IN. X sec. PER IN. X CANDELAS PER IN.

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I

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SEC PER IN . = • 0666 ! I I AREA BETWEEN LIMITS t1b and tit>• 4.60 SQ. IN.

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(2.165 X .0666) +.2 i

l!P ESTIMATE.fsl I I SEC. ~ER IN. = ·1"6"

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Chap 3 Par 10 Page 34 29 July 1971 AC 20-74 TYPICAL FLASHTUBE MEASUREMENT DATA SHEET Input Voltage - 14.0, Flash Capacitor 177 MFD.

Charge Voltage - 420 V., 15.6 Watt-Seconds Flash Rate - l per second.

o Vertical Angle Teat Distance - S.O ft.

Bn = Single flash reading x o2 x 5, (Multiplier= 125)

Horizontal Distribution Data HOR. METER NO. OF FLASHES AVG. READING READING INTEGRATED FOR SINGLE FIASH ~ ill 248.0 19.8 10 1.98 ...

10° 22.0 10 2.20 275.0 22.0 275.0 20° 10 2.20 19.8 24s.·o 30° 10 1.98 20.4 10 2.04 255.0 scf' 17.1 10 l. 70 212.0 13.7 171.0 60° 10 1.37 10° 11.0 10 1.10 137.0 11.0 80° 10 1.10 137.0 900 11.5 10 1.15 144.0 100° 12 .1 10 1.20 15C.O 11.5 10 l.15 144.0 120° 11.0 10 1.10 137 .0 13<>° 8.8 10 .88 110.0 TYPICAL FLASHTUBE MEASUREMENT DATA SHEET.

Fiere 3.9 Chap 3 Page 35(and 36) Par 10

AC 20-74 29 July 1971 l 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

29 July L971 AC 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 13 Page 2 EQll\'ALENT DESCRIPTION UNIT SYMBOL gUANTlTY ~

-

1u111en Rate cif Flow of Light lumens • watts x bllU X V{•,I Flux ~ 1 lumen/steradian :andelas • fo-,t.:andld x Point Source Uaht Power I Candela Intensity dlstlnc~ squared (1/,) canddas/tt Concentration of Intensity footlambert L Luminance 1 /" r,2 ,. __ ,,,_,1, ••. It ... 2 fro111 surface source l lumen/cm2 (brightneaa) lambert 2.054 candelas!in2 • car,d.elas~Hatan.:e l lumentf1.2 h·,•tcandles footcandle Surface Received Light E Illuminance squared l>ensity 106 mlcromeu,rs (,.a) R~tio of velocity=~ ::ictt:r • meter Distance Traveled During Wavelength • 109 nanom.!ters (nm) frequency of radiation

"

a Cycle • 1010 ang~cro!'!\lo (A~, surf.ac.E: arta/ steradians• steradian Total Solid Andes/411 Dimension Angles Two w Solid Angle dlstanc:E: 11uar•: (Sphere) jouleslS1t.: watt Electrical Energy Rate w Po11er y Eye Response to varying V(A) Luminous Wavelengths (Table 1,1) Efficiency

AC 20.. 74 29 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 11 11 is called "metamerism," and the two colors are called a metameric pair.

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 I tmgth. 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 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: 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 1

29 July 1971 AC 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 • This X • y • Y , and z • Z

---

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 ~ F.y AA 3 0

and the transmittance T • • · r;~ Ey T6A

r~i8 Ey A).

Page 2 .

/C lU-14 29 ·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 1 29 July 1971 AC 20-74 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.