AC 20-74 29 July 1971 'urves, a visual inspection through the entire area should be made to determine whether or not there are any noticeable shadows or areas where visual observation would indicate puestionable conformance. If any such questionable arcas die noted, further measurements should be made in those areas in demonstiate satisfactory coverage.
Redi Mile l'osition Light. A horizontal distribution from 70) degrees right to 70 degrees left " directly to the reur.
Three vertical distribution curve. from 90 degrees up to 90 degreus down through the following horizontal points: directly astern, i duprees lett of directly to the rear, and in degrees rishit of directly to the rear. Laboratory reports of such measurements should also include at least the followiug:
(1) A list of the test equipment and calibration dates for light standards which should show calibration against the lab working standard within the past 30 days, and the working staudard against the lab primary standard within the last 180 days. The laboratory primary standard should be traceable to the National Bureau of Standards.
(2) If a luminous-efficiency-correction filter is included, data adjustment for filter errors should be shown and substantiated.
(3) If transmittance measurements ate used, the data should show adjustment for the comparison in transmittance between any clear filter used during the intensity measurements and the transmittance of the colored filter. If a clear cover is used, it should have the identical shape as the colored cover.
Transmittance data should be shown on a computation sheet such as shown in Table ?.1. Also, íf a spectrophotometer is used it should be substantiated that the sample used in the measurements is representative of the actual light cover.
(4) When red glass is used, the data should show the temperature if light covers during measurements and data on the transmittance characteristics relative to temperature. Measured intensity values should 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°F. If no actual measurement is made with an ambient temperature of 100°F, extrapolation should be supported by data.
(b) When transmittance data 1s 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 3 Page 22 Par "
29 July 1971 AC 20-74
(5) A description of the procedure used to obtain intensity and tranamittance data, including the calculations. A diagram of the test set-up 18 desirable. This description and diagram should show:
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 Lighting 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. Color. Position fight color measurements require equipment such as described in Chapter 2, paragraph J. Aviation green contormance should be show 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 teat equipment with, when applicable, calibration dates.
(2) When red glass is used, the data should include the temperature 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 the glass 18 78°F.
If chromaticity-coordinate measurements are made, measured values should be adjusted to those corresponding to an outside cover glass temperature
(3) A description of the procedure used to obtain the color data.
A diagram of the test set-up 1s desirable.
Chap 3 Page 23 Par 9
AC 20-74 29 July 1971
3. ANTICOLLISION LIGHT DATA.
a. Intensity. Measurements for "effective intensity" require techniques as described in Chapter 2, paragraph 2.b. (3). The light may be white liane, on measured as a white light, and the intensity values adjusted according to the transmitlance of the red cover. The computation sheet used to determine the chromaticity-coordinates contains the data for determining the luminous transmittance of the red cover. If a clear cover is used in the intensity measurements, the ratio of the transmittances of the two covers me be used to correct the data.
To show field of coverage, a combination o! vertical and horizontal measurements is necessary. Figure 1.6 is a typical presentation of vertical elfective intensity distribution and is shown with the FAA minimum intensity requirements. Such curves are constructed from points representing separate effective intensity measurements.
To assure sufficient points to accurately draw the vertical distriburion curve, measurements are usuilly made at vertical angles of 430°, +20°; $10°, $5' and O. Ibree of nine such points are shown in Figure 3.6. To «btain 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 represents a single horizontal direction, there should be enough measurements to assure complete field of coverage. In other words, it should be substantiated that 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-Rey equation, the maximum value of effective intensity is obtained when t2 and t1 are choser so that the effective intensity is equal to the instantaneous intensity at t2 and t1- Io 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 t2 and [1 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 have examples of data and 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 the glass. As mentioned before, red glass decreases in transmittance with heat.
Page 24 Chap 3 Par 10
29 July 1971 AC 20-74 For short time flashes such as those produced by flashtube units, an integrating type photometer is generally used.
These instruments integrate the whole flash rather than should be followed. For typical flashtube measurements, the value or t2 - t, is negligible compared to u.¿ seconds.
Computed effective intensity for these lights is therefore maxibum when the entire flash 18 included. Effective intensity for short time flashes can be found by the following relation:
Footcandle-seconds (meter reading) x distance squared : 0.2 seconds 1250 To improve the accuracy, several flashes are integrated and an average 18 taken. Figure 3.9 is an example of typical flashtube measurement 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 E°C = 1/2 (420)2 (177X10-6) 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 1s convertible to candelas. The multiplier
(125) in the example results fron D2/0.2. In the tabled data, therefore, the single flash footcandle-second reading tines 125 gives 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 2.2. (1).
(2) Luminous-efficiency-correction filter data as discussed in paragraph 2.a. (2).
(3) Iransmittance 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. (5).
For anticollision lights, this information should also include the method used to determine "effective intensity."
Chap 3 Par 10 Page 25 443-651 0-71-3
AC 20-74 29 July 197!.
(6) For strobe sources, the spectral distribution data used in transmittance computations should be substantiated by data showing spectroradiometer measurements, or published data which can be shown to be applicable.
Color. The measurement for color of an anticollision light red rover is usually made with a spectrophotometer. In this measurement, the computation sheet (Table 2.1) should contain values for spectral distriburion which are representative of the light source being used. Pre-computed values for Ex. By.
and Ez are available for many type sources and are identified by color temperature. NBS Monograph 104 has several :amples.
The color temperature and the values for Ex, Ey, aud Iz must be accurately known if the results are to be dependable.
Laboratory reports which accompany the data should show at least the following:
(1) A. list of the test equipment with, when applicable, calibration dates.
(2) Temperature data as discussed in paragraph 2.b. (2).
(3) Procedure information as discussed in paragraph 2.b. (3).
chap :
Page 26 car 10
AC-20-71 29 July 1971 20° 20• 1=40 CANDELAS — Is 40 CANDELAS — 110• 30
LEFT RIGHT REAR IS UDINAL 140
POSITION LIGHTS, MINIMUM INTENSITY IN THE HORIZONTAL PLANE Chap 3 Par 10 Page 27
AC 20-74 29 July 1971
0.90 1 1.001- ABOVE 0.8012 HORIZONTAL 0.70 1€
0.50 IL 40
0.05 1 0.30 14 20° 30°
0.10 I T 15° 10°
HORIZONTAL 5' PLANE * 10° 15°
0.05 I 120° 30° 20• BELOW
HORIZONTAL
POSITION LIGHTS, MINUMUM INTENSITIES IN VERTICAL PLANES Figure 3.2 Chap 3 Page 28 Par 10
29 July 1971 AC 20-74
ANTICOLLISION LIGHTS, MINIMUM INTENSITY IN VERTICAL PLANE Figure 3.3 Date of I. C. Application:
Prior to 8/11/71 100 On or after 8/11/71 400 Chap 3 Par 10 Page 29
AC 20-74 29 July 1971 120ª 100° 80° 60° 40° 20° 20° 40*
TYPICAL HORIZONTAL INTENSITY DISTRIBUTION-POSITION LIGHT FIGURE 3.4 Chap 3 Page 30 Par 10
29 July 1971 AC 20~74 60° 20° - 20° - 40° - 60° - 80
TYPICAL VERTICAL INTENSITY DISTRIBUTION-POSITION LIGHT FIGURE 3.5 Chap 3 Par 10 Page 31
AC 20 - 74 IL6T KINS 6Z
ROTATING BEACON
EFFECTIVE INTENSITY DISTRIBUTION
28.0 VOLTS 1.67 AMPERES 50 RPM
AVIATION RED LENS 200 175
EFFECTIVE INTENSITY MINIMUM
INTENSITY
REQUIREMENTS 25 FIGURE 3.6 -30° -20° -10° +10° +20° +30°
DEGREES VERTICAL Chap 3 Page 32 Par 10
SHOWING EFFECTIVE INTENSITY CALCULATIONS EXAMPLES OF TYPICAL TIME-INTENSITY CURVES 29 July 1971 ow SECONDS PER INCH = .0666 CANDELAS PER INCH = 200 THIS CURVE TAKEN AI -5° ELEVATION (B) THIS CURVE TAKEN AT DO ELEVATION (A) 1200 11200-
AREA BETWEEN LIMITS AREA BETWEEN LIMITS 112 - 41 L AND 12 = 2.90 SQ. IN. = 1.109 IN. 62-41. 1 AND 12 = 3.50 SQ. IN. = 1,056 IN.
1000 2.90X 200x .0666 1000- 3.50 × 200 × .0666 = 173
(1.109 x .0666) +.2 (1.056 x .0666) + .2 FIGURE 3.7 141 X 1.12 (HEAT CORRECTION 173 X 1.12 (HEAT FACTOR) = 158 CANDELAS CORRECTION FACTOR) = 800-- • 194 CANDELAS -600- 400 400. ESTIMATE LINE IS CLOSE ENOUGH TO ESTIMATE LINE IS CLOSE 173 FOR PRACTICAL ENOUGH TO 141 FOR CONSIDERATION
PRACTICAL CONSIDERATION -200- Page 33 -1,109 ". 1.056"•
- 0666 SEC.- .0739 SEC. 12 .0703 SEC.