NATIONAL BUREAU OF STANDARDS REPORT

10i56

COMPARATIVE TABLE

CHROMATICITY REQUIREMENTS OF U.S. AND INTERNATIONAL

SPECIFICATIONS AND STANDARDS

FOR

AVIATION SIGNAL LIGHT COLORS

Prepared for

Airport Lighting and Marking Panel

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

of the divisions and sections engaged in technical work. In general, each section is engaged in

specialized research, development, and engineering in the field indicated by its title. A brief

description of the activities, and of the resultant reports and publications, appears on the inside

of the back cover of this report.

Electricity and Electronics. Resistance and Reactance. Electron Tubes. Electrical Instru- ments. Magnetic Measurements. Process Technology. Engineering Electronics. Electronic

Instrumentation. Electrochemistry.

Optics and Metrology. Photometry and Colorimetry. Optical Instruments. Photographic

Technology. Length. Engineering Metrology.

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Engines and Lubrication. Engine Fuels.

Atomic and Radiation Physics. Spectroscopy. Radiometry. Mass Spectrometry. Solid

State Physics. Electron Physics. Atomic Physics. Nuclear Physics. Radioactivity. X-rays.

Betatron. Nucleonic Instrumentation. Radiological Equipment. AEC Radiation Instruments.

Chemistry. Organic Coatings. Surface Chemistry. Organic Chemistry. Analytical Chemistry.

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Mechanics. Sound. Mechanical Instruments. Fluid Mechanics. Engineering Mechanics.

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Data Processing Systems. Components and Techniques. Digital Circuitry. Digital Systems.

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Gas Liquefaction.

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Propagation Services.

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Research.

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

NBS PROJECT NBS REPORT

0201-20-2303

0201-20-2301+

0201-30-2328

January 1956 1+1+56

Comparative Table

Chromaticity Requirements of U.S. and International

Specifications and Standards

for

Aviation Signal Light Colors

Prepared for

Airport Lighting and Marking Panel

by

F. C. Breckenridge

Photometry and Colorimetry Section

Optics and Metrology Division

<NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication, re Approved for public release by the

unless permission li director of the National Institute of

25, d. c. suchper Standards and Technology (NIST)

cal ly prepared if tl On October 9, 2015

in part, is prohibited

andards, Washington

port has been specifiiport for its own use,
I I
Symbol Specifications Included in Tables Date

an-c-56

an-c-56

Amend3

Fed. Std. No.

Amend-1

MIL-C-25050

(ASG)

I. C.A.O

C • I. E»

U. S. Specifications and Standards

Army-Navy Aeronautical Specification, Colors;

Aeronautical Lights and Lighting Equipment.

Ditto

3 Federal Standard, Colors, Aeronautical

Lighting

Military Specification, Colors, Aeronautical

Lights and Lighting Equipment, General

Requirements for

Proposed U.S. Standard for the Colors of

Signal Lights; Part I, Definitions Underlying the Specification of Colors far

Signal Lights

International Standards and Recommendations

International Standards and Recommended

Practices, Aerodromes, Annex lij. to the

Convention on Civil Aviation

International Commission on Illumination,

Recommendations of the 13th Session,

1.3*3 Colors of Signal Lights

25-YL-U2

6-YE-U5

27-MIH-5L

29-X-5U

1955

1-IX-53

1955
_

’ 0®

.
Explanatory Statement

The accoupanying tables show the equations used as boundaries for

the aviation signal-light colors in the United States together with

the corresponding equations used in the standards of the International

Civil Aviation Organization and the 1955 Recommendations of the International Commission on Illumination, All the equations are expressed

in the coordinates of the C.I.E, system* which is the system used in

all the specifications* but since the R-U-C-S equivalents of the C.I.E,

recommendations are not available elsewhere* a column has been added

to give these also.

The purpose of these tables is to bring out similarities and differences between the several specifications; hence* instead of repeating

an equation for each specification in which it occurs, repetitions are

emphasized by references to the appropriate columns. To further facilitate comparisons, certain conventions which had already been followed

in the form of all of the international specifications have been applied

to the U. S. specifications also. These include the elimination of z*

the selection of the independent variable to keep the coefficient less

than 1,000* and the placing of the constant ahead of the variable on

the righthand side of the equation. When necessary* the original

equations in the U. S. specifications have been transformed to conform

with these conventions but such transformations do not change the

mathematical significance of the equations.

Even when the specifications are in the same form* it is still

difficult to appraise the difference between two chromaticity boundaries from their equations. The tables are* therefore* accompanied

with a set of U diagrams showing the boundaries of the several colors

in the different specifications. Three of these diagrams were originally prepared to show how the Proposed U. S. Standard is related to

existing specifications and for that reason these diagrams include the

boundaries of several specifications that are not used for aviation

purposes and are not included in the tables. Figure 1 shows the entire

mixture diagram and gives a general view of the relationship of the

reds at the bottom, the greens at the top* and the blues on the left

to the white/yellow region in the center. Figure 2 presents the new

C.I.E. treatment of the central yellow/white region. Figure 3 shows

the boundaries for white in different specifications. Figure k compares the hue requirements for red and yellow in the U. S. and international specifications.

The C.I.E. yellow/white recommendations* Figure 2* require some

explanation. The entire area within the outer boundaries* including

the cross-hatched portions* is regarded as essentially one color and

any part of this area is recognizable* under usual conditions of
* ! : ' V
-2-

observation, as being neither red nor green. To this entire range

of chromaticities the term tyellow/white’1 has been applied. Under

favorable conditions, it is practicable to divide this region into

two regions, that is a yellow and a white, the boundaries depending upon the conditions of use. These restricting boundaries are

shown in Figure 2. In the case of the distinguishable white, it is

also necessary to insure a reasonable separation of signal chromaticities by a suitable selection of limit filters so that only the

redder yellows will be seen when the white signals are in the yellower part of the allowed white region. This arrangement is necessary to provide for yellowing of the white signals as their intensity

is lowered.

Comparative Table of IdentificationLight Color Specifications

Specification an-c-56 an-c-56 Federal u. s. Original Amended Standard Standard

Color Boundary- No. 3

19U2 19l*3 1951 Proposed

Red Purple x + y = 0,999 do an-c-56 x + y = 0.998

Yellow y - 0.287 do an-c-56 x - y = o.iao

Yellow Red y = 0.370 do an-c-56 y

= 0,382

White x + y = 0.995 do an-c-56 x+y-0. 872+0. 20Gx

Green y * 0.U23 do x = 0.570 x = 0.955

Green Yellow x = 0,312 do an-c-56 y = 0.730(l-x)

White x*-0.2lU+0*833y do an-c-56 x = o.U25y

Blue y*+0. 663-0. 83 3x do an-c-56 y*0. 500-0. 500x

White

(lunar) Yellow x = 0.1J;0 do an-c-56 x=0. 250+0. 500y

Blue x = 0.2U0 do an-c-56 x-0. 350-0. 300y

Green y - y0

= 0.0x5 do an-c-56 |x - x0 | = 0,008

y - y0 = 0,008

Purple y0 - y = 0.015 y0 - y

- 0.01*5 do |x - x0 j = 0.008

y0 - y

= 0.008

Signal Red

Purple X + y = 0,999

White y = 0.301*

Signal Green

Yellow X = 0.312

White x-0.2Hn-0.833y*

Blue y=+0. 663-0. 833x *

do, same as previous column.

same as identification green.

Requirements of MIL-C-25050 are identical with those of AN-C-56 Amended.
. . ‘
Comparative

Table

of

Aviation

Signal

-Light

Color

Specifications

• © w ©

W ID I so • & u a

H* rH I *H

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ou

X >4

pH£

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II

sceess ss c IfOOCfeVSlcy | I £ f ft £ & CV ? 9 3 i <f © W O © fH © 8 W pH © O unm

X

© © O © © © © © © . © © © ©

U U ^ ti li li J

i i o i T i i 3 5 M- 5 S3 5 3

revision

x+y

=

0.992

**Proposed

revision

|x

-x

n|

=

0.008,

y

-y

Q

=

0.008,

y

0

-y

=

0.008

#Ax"

=

x"

-

0.075

revision

x+y

=

0.872

+

0.200x,

##Recomm

ended

Practice

0 +.1

+.3

+ .2

Y"

+ J COLOR

TEMPERATURE

^co

"*"24 000* K *(0 000 8 * 6 500°

0* 4 800®

3500® * 2850°

<- 1900°

<- 1500°

-.2

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,<• 1000 '

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<- 600 0

-5
IV
+.10+ .10

+.08

+.06

+ .04

+.02

.00

-.02

.04

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Y

-.08

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-.12

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.16

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.22

-.02 .00 +.02 +.04 +.06 +.08 +.10

I

X

FIGURE 2

I

A

570 —

580 —

600-

610

:--3

120 A

-—.4

640-r

68 0=

:

! y ! / 590 —

r

;

Mill h

- 2

> \

'

\

COMPARISON OF LIMITS FOR RED AND YELLOW

SIGNAL LIGHT COLORS

U. S. and INTERNATIONAL SPECIFICATIONS

R-U-C-S DIAGRAM <

Y"

0

y y \ / /

\

\ \

\ \

/ /

/ / ^ / / /o^ /

/

/ / / / / /

/ / / /

Co'c' *9' ’OVr *9' *9 v v °

O' X V \> X X> V

w w5

,'S' VJ < ^7 A r '-O' \ 9 V \0 <o V V <b yy

**

^ <*-/PVy \x ^ ^ o <c V® <o <9 „ T ^ ^ , <b- \ V O' <$' Cj *9" 4*^ O' Cl- O' O' O' *9'

. *9' *9'

(j. „\. 6v v U,v tx.v Os- Os- A Os- Os- Os

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<b' <s

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GENERAL AVIATION MARINE HIGHWAY RAILROAD IDENTIFICATION

A

—570

;^-580

;^-590

:~ 600

- 7

- 61

0

E-620

;E- 64 °

i^eso

FIGURE 4
.
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

for making measurements consistent with these standards; the determination of physical constants

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

devices, and structures; advisory services to Government Agencies on scientific and technical

problems; invention and development of devices to serve special needs of the Government; and the

development of standard practices, codes, and specifications. The work includes basic and applied

research, development, engineering, instrumentation, testing, evaluation, calibration services, and

various consultation and information services. A major portion of the Bureau’s work is performed

for other Government Agencies, particularly the Department of Defense and the Atomic Energy

Commission. The scope of activities is suggested by the listing of divisions and sections on the

inside of the front cover.

Reports and Publications

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publications should be addressed to the Office of Scientific Publications, National Bureau of

Standards, Washington 25, D. C.