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NATIONAL BUREAU OF STANDARDS REPORT

4542

CANDLEPOWER DISTRIBUTION AND COLOR CHARACTERISTICS

OF A DOUBLE OBSTRUCTION LIGHT

by

Robert T. Vaughan

to

Airways Engineering Division

Office of Federal Airways

Civil Aeronautics Administration"

<NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
U. S. DEPARTMENT OF COMMERCE

Sinclair Weeks, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director

THE NATIONAL BUREAU OF STANDARDS

The scope of activities of the National Bureau of Standards is suggested in the following listing

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Radio Standards. High Frequency Standards. Microwave Standards. • Office of Basic Instrumentation • Office of Weights and Measures
NATIONAL BUREAU OF STANDARDS REPORT

CANDLEPOWER DISTRIBUTION AND COLOR CHARACTERISTICS

OF A DOUBLE OBSTRUCTION LIGHT

by

Robert T. Vaughan

Photometry and Colorimetry Section

Optics and Metrology Division

NBS PROJECT

0201 - 30-2328 February 1$56

NBS REPORT

4542

NBS Test 21A-7/55

to

Airways Engineering Division

Office of Federal Airways

Civil Aeronautics Administration

Department of Commerce

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication, repr

unless permission Iso 25 ,D.C, Such perm

cal ly prepared If thi

Approved for public release by the

director of the National Institute of

Standards and Technology (NIST) on October 9, 2015

1 part, is prohibited

idards, Washington

>rt has been specifiort for its own use,

Candlepower Distribution and Color Characteristics

of a Double Obstruction Light

by

Robert T. Vaughan

1. SCOPE

This report presents the results of a study of the

candlepower distribution and color characteristics of a double obstruction light. The study was made primarily

to provide a basis for evaluating the performance of a

neon obstruction light relative to that of the incandescent obstruction lights in common use. The characteristics of the neon obstruction light, designed for use on

the catenary of a transmission line, have been reported

in NBS Report 4441.

2. DESCRIPTION OF EQUIPMENT TESTED

The equipment tested, shown in figure 1, was taken

from stock at Washington National Airport and consists

of

(A) A double obstruction light fitting manufactured

by the A.G.A. division of the Elastic Stop Nut Corporation, Elizabeth, N. J. The fitting bears the following

marking: "ELIZABETH A 1 G

1 A NEW JERSEY.

(B) Two red cover glasses, each a cylindrical fresnel lens closed at the top.

One glass, designated for the purposes of this test

as "lens A", is marked

"AP 3522-2-R

K

Made in U.S.A."

This glass was presumably manufactured by Kopp Glass,

Inc., Swissvale, Pa. It has inside vertical prisms de°

signed to eliminate the shadows of the lamp filament supports, and it is approximately 4 inches in effective

height and 3 1/2 inches in outside diameter at the center

belt.
n
- 2 -

The other glass, designated as H iens E”, is marked

”PYREX T.M.REG." On the underside of the flange the following marking appears:

”PYREX T.M. REG. U. S. PAT. OFF. MADE IN U. S.A.

530018” This glass was presumably manufactured by the Corning

Glass Works, Corning, N. Y. It is approximately 4“ in

effective height and 4” in outside diameter at the center

belt.

(C) Three G.E. 111A 21/TS traffic signal lamps rated

at 111 watts, 120 volts.

3. TEST PROCEDURE

The three lamps were seasoned at their rated voltage,

120 volts, and the total luminous flux from each was measured in a 60-inch integrating sphere at energizing vo]*a?e3

of 110 volts, 115 volts, and 120 volts. The values recorded

were converted to ”lumens per watt”, and, as £1 own in figure 2, a graph of lumens per watt vs. energizing voltage was

plotted for each lamp. The abscissa of the intersection of

each of these curves with the curve representing the rated

lumens per watt indicates the voltage at which each lamp

should be operated to assure that it would be operating at

its rated efficiency and hence at its normal color temperature. All candlepower and color measurements were made with

each lamp operating at the test voltage so determined. Since

no method is provided for focussing the unit, it was tested

as received.

To provide measured horizontal and vertical rotations

of the test unit, the unit was mounted in a special fixture

on the table of a goniometer. The primary axis of rotation

was horizontal and normal to the photometric axis. With the

goniometer set at the 0°,C° position the fitting was mounted

with the axes of the lenses lying in a plane perpendicular

to the photometric axis, and with the axis of the right-hand

lens, as viewed from the photocell, coincident with the ver=

tical axis of the goniometer. The lenses were oriented so

that the notches in the flange of each were in the transverse

plane and the lettering on the top of the lenses was right

side up when viewed from the photometer side of the goniometer.

The lamp-lens combination to be measured was mounted in the

right-hand position on the fitting, and the remaining lens,

with no lamp, was mounted in the left-hand position.
' 1 ; -

... ..
- 3

-

The measurements were made with an automatic photometer, the recording element of which is a Leeds & Northrup

recording potentiometer driven in synchronism with the

goniometer table on which the unit under test is mounted.

The photometric distance was 10.0 meters.

The photometer was calibrated with standard filter No.

3639 and v/ith standard lamp No. NBS 3315 at a distance of

2.0 meters. The calibration includes a correction factor

which is the ratio of the rated lumens of the lamp to the

lumens produced by it when operating under the test conditions at its rated color temperature. This calibration

has been recorded on the candlepower distribution chart as

a line showing the candlepower of the test unit which would

give an illumination at the photocell equivalent to that

given by the standard lamp multiplied by the correction

factor

.

Since the luminous transmittance of the type of red

glass of which the lenses are made is a function of its

temperature, a record was made to determine the time required after the lamp was energized for the transmittance

of the lens to reach equilibrium. This record, shown in

figure 3? indicates that at an ambient temperature of 75°F

the transmittance of the lens became stabilized after the

lamp had been operated at its test voltage for a period of

about 40 minutes. Each lamp-lens combination was operated,

therefore, at its test voltage for a period of at least one

hour before the candlepower measurements were recorded.

Measurements were then made of the following lamplens combinations in the order indicated.

Measure- Lamp Figure

ment No. No. Lens Traverse No.

1 1 A Vertical at 0

C Eoriz. 4

2 1 A Horizontal at +7.0° Vert. 5

3 2 A Vertical at 0° H

s0

4 2 A Horizontal at +7«$ c Vert. 7

5 3 A Vertical at 0° H 8

b 3 A Horizontal at +9*5° Vert. 9

7 1 B Vertical at 0° H 10

8 1 B Horizontal at +8.5° Vert. 11

9 2 B Vertical at 0° H 12

10 2 B Horizontal at +9.7° Vert. 13

11 3 B Vertical at 0° H 14

12 3 B Horizontal at +8.8° Vert. 15

13 3 B Set of 8 Vert, traverses

at 45° Horiz. intervals 16

14 3 A Set of 8 Vert, traverses

at 45° Horiz. intervals 17
"

-

'

.

' ‘ '

.
- 4 -

Because lamp No. 3 was found to most nearly approximate the

•average* of the three lamps, it was selected for the two

sets of vertical traverses, measurements No. 13 and 14.

Vertical angles above the horizon were considered as positive angles; ''hose below the horizon, as negative angles.

Using a Lummer-Brodhun photometer head, trained observers compared the chromatlcity of the light from the

test unit with that transmitted from a standard lamp at

2350°K through standard filters whose chromatlcity coordinates for light of that color temperature are known.

4. RESULTS

The

tion was

maximum

found to

candlepower for each

be as follows:

lamp-lens combina

Lamp Lens Max cp. Vert. Horiz

.

Fig

1 A 1C4 +7.0® C° 4

2 A 102 +7.9° 1 72 ° 7

3 A 115 +6.5° 225° 17

1 3 90 +8.5° 30° 11

2 B 63 +9.7° 177° 13

3 B 73 +8.8® 348® 15

On the candlepower distribution charts, there is a

small discrepancy between the calibration marks and the

grids, amounting at most to 1.9$, but this can be disregarded in view of the large variations in the candlepower

of the unit with different lamps and lenses.

In figure 17, the narrow peaks in the candlepower distribution curves occurring between the vertical angles +82°

and +85° are due to an image of the C-9 filament formed by

the top section of lens A. Since this, region is one of

little imDortance, the variations in the candlepower due

to the image are of little significance.

The results of the chromaticity comparisons are shown

in figures 13 and 19. The chromaticities of the standard

filter and lamp combinations are shown in the figures as

circles. The chromaticity of the test unit differs from

each of the known chromaticities in the sense indicated by

the arrow in each case.
-

' ; -

'

-
- 5

-

The chromatic ity of the light transmitted by each of the

lenses using a lamp of the recommended type at its rated lumens per watt was found to be within the limits for aviation

red as defined in Specifications AN-C-56, Fed. Std. No. 3> and

MIL-C-25050 (ASG)

.

5. DISCUSSION

There is a considerable difference between the transmittance of pale-limit red glassware and that of ware of minimum

acceptable transmittance. This difference in transmittance

causes a corresponding difference in the candlepower of the

units on which the glassware is used. It is desirable, therefore, to know how the two lenses measured compare in transmittance with the average for each type to be expected in

service in order to know how to interpret the measured values

given in this report.

A good approximation to the transmittances for the measured lenses can be estimated from the results of the color

tests. Studies of the characteristics of selenium glass

filters have shown a correlation between their redness and

tr? "smittance, the relationship depending upon the color temperature of the light source. The color temperature, in turn,

is a function of the lamp efficiency. The normal color temperature for a gas-filled tungsten lamp operating at the rated

lumens per watt of the test lamp (11 .

7

lpw) is 2750°K. For a

light source of this color temperature, the color of lens A

is characteristic of glass having a transmittance ratio of

0.18 and that of lens B corresponds to glass having a transmittance ratio of 0.12.

Obstruction light lenses are classed in the color specifications as thicksectioned ware for which the transmittance

requirements of Grade D are stipulated. This requirement

allows a minimum transmittance ratio of 0.130 for a light

source of 2854°K (Spec. AN-C-56, Table IV, Non-diffusing ware,

Type I.)With pale-limit ware, the transmittance ratio may be

as high as 0.31 which is 2.4 times the minimum.

The transmittance value estimated for lens B would drop

even more below the minimum permitted by the specifications if

the transmittance measurements were made with a light source of

color temperature 2850°K as prescribed in the specifications.
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- 6 -

On the basis of the approximate estimates made above,

the candlepower of lens B should be regarded as a minimum

for incandescent obstruction light units of its design,

while the candlepower of lens A is approximately 0.6 of

the maximum to be expected from the palest acceptable lenses

of its type.


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THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

The functions of the National Bureau of Standards are set forth in the Act of Congress, March

3, 1901, as amended by Congress in Public Law 619, 1950. These include the development and

maintenance of the national standards of measurement and the provision of means and methods

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and properties of materials; the development of methods and instruments for testing materials,

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