U S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Building Physics Division

Washington, DC 20234

April 1983

;co

Sponsored by

The Occupational Safety and Health Administration

U.S. Department of Labor

Washington, DC 20210
i'-
NBSIR 83-2694

SOME CRITERIA FOR COLORS AND

SIGNS IN WORKPLACES

NATIONAX, BUREAtf OP STANDAHDS

UBRARV

MAY 5 1983

r>£>i c

9

Robert A. Glass

Gerald L. Howett

Karen Lister

Belinda L. Collins

U S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Building Physics Division

Washington, DC 20234

April 1983

Sponsored by

The Occupational Safety and Health Administration

U.S. Department of Labor

Washington, DC 20210

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

ABSTRACT

The use of safety-related visual displays such as signs and colors In

workplaces Is discussed. The discussion Includes a review of relevant national

and International standards for safety colors and signs. It also Includes a review of measures of spatial resolution In human vision, as well as of color

sensitivity and color appearance. In addition, research on the effectiveness

of safety signs, symbols, and colors Is reviewed. Based on the Initial literature review, the appearance of safety colors under energy-efficient light

sources was Identified as an area for detailed research. As a result, a laboratory study was conducted In which the color appearance of 45 different

color samples under five light sources Including energy efficient ones was determined for seven subjects. The color samples were contained In four color

series: standard safety colors; experimental colors; retroref lectlve and

retroref lectlve-f luorescent colors; and fluorescent-only colors. The results

Indicated the existence of a set of colors which was more Identifiable under

all light sources than the current standard safety colors. This set contains

a number of fluorescent and retroref lectlve colors, unlike the current safety

colors. Recommendations are made for further research. Including field

research, to determine the effectiveness of the suggested color set on safety

signs under an even broader range of lllumlnants. The need to assess color

appearance under mixed light sources Is also addressed.

Keywords: Chromatlclty , color, color appearance, energy-efficient lights.

Illumination, light source, safety, safety signs, safety symbols,

visual acuity, visual sensitivity.

Ill
FOREWORD

This report is one of a series documenting the results of NBS research in

support of the Occupational Safety and Health Administration (OSHA) , in fulfillment of OSHA contract No. lAG No. J-9-F-7-0146 entitled "Criteria for

Signage in Workplaces." The report summarizes research conducted in the

period December 1977 through April 1983.

We wish to acknowledge with special thanks the Interest, cooperation, and

encouragement of the sponsor's Technical Project Officer, Mr. Tom Seymour,

OSHA Office of Standards Development.

DISCLAIMER

Certain commercial equipment, instruments, or materials are Identified in

this report in order to adequately specify the experimental procedure. Such

identification does not imply recommendation or endorsement by the National

Bureau of Standards, nor does it imply that the materials or equipment identified are necessarily the best available for the purpose.

iv
TABLE OF CONTENTS

Page

1. INTRODUCTION 1 1.1 BACKGROUND 1 1.2 EXISTING STANDARDS 1 1.2.1 Proliferation of Standards 3

1.2.2 Decision Criteria for Improving Visual Alerting

Systems 5

1.2.3 Measurement of Compliance 5

2. VISUAL REQUIREMENTS FOR SAFETY COMMUNICATION 7

2.1 BACKGROUND 7

2.2 MEASURES OF SPATIAL RESOLUTION IN HUMAN VISION 8

2.2.1 Specific Variables 8

2. 2. 1.1 Minimum Distinguishable 8

2. 2. 1.2 Mlmlmum Separable 8

2. 2. 1.3 Vernier Acuity 9

2. 2. 1.4 Minimum Recognizable 9

2. 2. 1.5 Contrast Sensitivity 9

2.2.2 Variables Affecting Resolution 9

2. 2. 2.1 Illumination Level 10

2. 2. 2. 2 Retinal Location 10

2. 2. 2. 3 Spectral Composition of Illumination 10

2. 2. 2. 4 Orientation 10

2. 2. 2. 5 Viewing Distance 11

2.3 COLOR SENSITIVITY AND COLOR CODING 11

2.3.1 Color Sensitivity 12

2.3.2 Visual Adaptation 15

2.3.3 Specification of Color Appearance 16

2.3.4 Color Coding 19

2.4 SIGN PERCEPTION 20

2.4.1 Background Research and Practice 20

2.4.2 Observed Sign Use ' 20

2.4.3 Symbol Sign Research 21

3. LABORATORY STUDY OF COLOR APPEARANCE UNDER DIFFERENT LIGHTS 28

3.1 BACKGROUND 28

3.2 METHOD 28

3.2.1 Subjects 28

3.2.2 Apparatus 29

3.2.3 Procedure 29

4. RESULTS 37

4.1 FREQUENCY DISTRIBUTIONS 37

4.2 COLOR SHIFT DATA 65

5. DISCUSSION 71

5.1 RECOMMENDATIONS BASED ON SAFETY COLOR RESEARCH 71

5.2 SUPPORTING RESEARCH 73

V
TABLE OF CONTENTS

Page

6. ElECOMMENDATIONS 76

6.1 APPLICATIONS TO THE WORKPLACE 76

6.2 PROBLEMS OF COMPLIANCE 76

6.3 RECOMMENDATIONS FOR FURTHER RESEARCH 79

6.4 CAPSULE SUMMARY 80

7. REFERENCES 81

APPENDIX A: ADDITIONAL DETAILS OF THE ILLUMINATION

LABORATORY 87

APPENDIX B: LIST OF DOCUMENTS COMPLETED DURING THE OSHA/NBS RESEARCH .. 88

vi
LIST OF TABLES

Page

Table 1. OSHA Safety Sign Requirements 2

Table 2. Coding Practices from Internal and U.S. Safety Sign

Standards 4

Table 3. Average Horizontal and Vertical Foot-Candles for Each

Light Source Measured for a Horizontal and a Vertical

Surface 30

Table 4. Experimental Color Samples — Series 100 to 400 31

Table 3. Color Frequency Charts — 100 Series 38

Table 6. Color Frequency Charts — 200 Series 42

Table 7. Color Frequency Charts — 300 Series 46

Table 8. Color Frequency Charts — 400 Series 48

Table 9. Tabulation of Colors Included as Second Color In a Color

Blend Response 51

vll
LIST OF FIGURES

Page

Figure 1. Confusion lines for dlchromats 14

Figure 2, CIE chromatlclty diagram containing the ANSI standard

safety colors Illuminated by daylight 18

Figure 3. Symbols suggested for safety messages 23

Figure 4. Spectral power distributions of experimental light sources 31

Figure 5. Design details of Illumination color laboratory 34

Figure 6. Percentage of trials In which designated color samples were

Identified as red under HPS 55

Figure 7, Percentage of trials In which designated color samples were

Identified as red under LPS 56

Figure 8. Percentage of trials In which designated color samples were

Identified as red under MH 57

Figure 9. Percentage of trials In which designated color samples were

Identified as red under fluorescent 58

Figure 10. Percentage of trials In which designated color samples were

Identified as red under tungsten 59

Figure 11. Percentage of trials In which designated color samples were

Identified as orange under LPS 60

Figure 12. Percentage of trials In which designated color samples were

Identified as orange under HPS 61

Figure 13. Percentage of trials In which designated color samples were

Identified as orange under MH 62

Figure 14. Percentage of trials In which designated color samples were

Identified as orange under fluorescent 63

Figure 15. Percentage of trials In which designated color samples were

Identified as orange under tungsten 64

Figure 16. Color shift data — tungsten to LPS 66

Figure 17. Color shift data — tungsten to HPS 67

Figure 18. Color shift data — tungsten to MH 68

vlll
LIST OF FIGURES

Page

Figure 19. Color shift data — tungsten to fluorescent 69

Figure 20. Chromaticities of standard ANSI colors illuminated with

HPS light 78

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1 . INTRODUCTION

1 . 1 BACKGROUND

Warnings and other safety-related messages are typically communicated by visual

displays, both within fixed workplaces and around temporary work sites, indoors

and outdoors. Safety-related visual displays usually perform two functions:

alerting personnel to the presence of some situation requiring their attention;

and tranmitting further information concerning the nature of this situation

and/or the action to be taken by the viewer. A visual display may be used to

communicate information by means of various components such as color, overall

shape, verbal legends, and non-verbal graphic symbols. To accomplish the two

basic goals, the overall display (color and shape) should be as attentionattracting as possible. Furthermore, the elements carrying the specific

information (legends and symbols) should be as concise, unambiguous, and

understandable as possible, and should be visible at the appropriate viewing

distance.

Although requirements and standards for visual displays, including warning

signs, have been in existence for a long time, the research base for these

recommendations is sometimes inadequate. In particular, the use of energyefficient light sources, such as high- and low-pressure sodium can distort

color noticeably, thus reducing the effectiveness of color coding in safety

displays or signs.

The present report will outline some requirements for effective signs and

present some preliminary data on the recognizabillty of safety colors under

different light sources, including several energy efficient sources.

1.2 EXISTING STANDARDS

The Occupational Safety and Health Act of 1970 had two sections dealing with

safety colors, signs, and tags. Section 1910.144, The Code of Federal Regulations (CFR) , 29, Labor, Part 1910.144, contained a Safety Color Code for Marking Physical Hazards, while Part 1910.145, contained Specifications for

Accident Prevention Signs and Tags. Some of these recommendations have since

been partially deleted (Code of Federal Regulations, 29, 1981), although the

regulations still provide general sign and color requirements for safety.

(Part 1926.200, Subpart G provides specifications for signs, signals, and

barricades for the construction industry.) The Occupational Safety and Health

Administration (OSHA) (Code of Federal Regulations, 29, 1981, p. 360) defines

a (safety) sign as a surface "prepared for the warning of, or safety instructions of, industrial workers or members of the public who may be exposed to

hazards. Excluded from this definition, however, are news releases, displays

commonly known as safety posters, and bulletins used for employee education".

Existing OSHA requirements are summarized in table 1. The development of any

new performance-based standards or guidelines requires research on the effectiveness of safety colors and signs under a variety of illuminants including

the energy efficient light sources. This need is addressed in the present

report.

1
Table 1. OSHA Sign Requirements—1910.144, 1981

COLOR MEANING APPLICATION

Red Danger Safety cans Portable cans with

flammable liquids

Barricades

Stop Emergency stop button

or switches

Yellow Caution Designate caution

Mark physical hazards

TYPE SIGNS COLORS

Danger Indicate presence of immediate

hazards;

Red, black, and white

Caution against unsafe practices Yellow and black

Safety Instructions Indicate general

instructions and suggestions

relative to safety messages

White and green

Slow Moving Vehicles Unique Identification for vehicles Fluorescent yellowwhich by design move slowly on orange with darkpublic roads red border

Biological Hazard Signify actual or potential presence

of a biohazard; identify equipment,

container rooms, materials, experimental animals which contain or are contaminated with viable hazardous

agents

2
OSHA’s interest is not confined to the Occupational Safety and Health Standards

mentioned above, however. At this time, there are over one hundred other

requirements in the General Industry Standards for signs, markings, or other

color/legend associations. Yet, there is no requirement for adherence to a widely accepted safety sign or color standard, nor are there any methods for

measuring compliance.

Three basic problems exist in the consideration of color/legend standards

today:

1. There is a growing proliferation of requirements at the international,

federal, and state levels, as well as at the voluntary standards level,

addressing different aspects of the color/legend problem.

2. There is often a lack of experimental research to support the criteria

for these requirements.

3. There are no formalized procedures for measuring compliance with the

requirements.

1.2.1 Proliferation of Standards

Over the years, various agencies and groups evolved practices and standards for

safety-related visual displays. These guidelines include specifications for

color, shape, word legend, and symbols. Although some features are common to

the various systems, such as the use of red to indicate "danger" or "stop", the

systems are not necessarily consistent. The result is the repeated exposure of

the population to signs and displays which follow contradictory conventions,

thus resulting in confusion and possible danger. Consequently, the user cannot

attach any single. Invariant meaning to colors, shapes, or symbols used in the

visual displays encountered every day. The adoption of a single, unified system would allow more rapid and more certain recognizability of the meanings of

visual displays and thereby contribute to the safety of both workers and the

general population.

To complicate matters further, both the American National Standards Institute,

ANSI, and the International Organization for Standardization, ISO, have drafted

voluntary standards for safety signs and displays. The ANSI Z35.1 (1972) Standard provides specifications for safety signs while the Z53.1 (1979) Standard

provides specifications for safety colors to be used on these safety signs.

The ANSI Z35 and Z53 committees have recently been combined to form the Z535

Committee on Safety Signs and Colors. This committee is currently updating

the Z53 (Color) Standard, and the Z35 (Sign) Standard, and will issue them as the Z535.1 (Color) and Z535.2 (Sign) standards. This committee is also

drafting Standards for Safety Symbols (Z535.3) and Product Alerting Signs

(Z535.4). Within the ANSI Z35 (1979) framework, the following conventions

regarding color were specified: Red = danger, stop; Yellow = caution;

Green = location of first aid, safety; Blue = general information. A third

hazard category is proposed in current Z535.2 and Z535.4 drafts which would

use Orange for warning. These provisions are outlined in table 2.

3
Table 2. Coding Practices from International and U.S. Safety Sign Standards

I SO/ EEC CANADIAN U.S.*

Red Prohibition Prohibition, Danger o Danger

o Stop

o Fire & Emergency

Orange — — 0 Dangerous Machine

o Energized Equipment

o Warning - Proposed

Yellow Warning Caution o Caution

- Storage for Flammables

o Containers for Explosives,

or Unstable Materials

- Radiation

o Highway

Green Information Emergency Information o Safety Information

o First Aid & Safety Equip,

o Highway - square, rect.

Blue Mandatory Action Mis cellaneous 0 Information

0 Bulletin Boards

o Railroad

Black Mandatory Action

* Adopted from ANSI Z35 and DoT (1971).

4
The ISO TC-80 on Safety Signs and Colors developed a draft standard (1978)

which specifies color and symbol sign configuration. These provisions are also summarized in table 2. It is immediately apparent from inspection of

table 2 that the ANSI and OSHA standards use color to code the level of hazard,

with red for danger and yellow for caution, while ISO uses only yellow to code

the presence of a hazard. Red is reserved for prohibition. Both set of standards agree on the use of green for safety and blue for general informational

signs, although ISO specifically identifies a "mandatory action" category, using

blue to code information such as "personal protective gear required." The

Canadian Treasury Board Standard (1980), however, uses black for this latter

category. In addition, the ANSI Z35 Standard relies upon word messages to

communicate hazard warnings while the TC 80 Standard uses symbols exclusively.

1.2.2 Decision Criteria for Improving Visual Alerting Systems

The proliferation of existing standards emphasizes the need to develop a research base for decisions about effective visual alerting displays for

safety. Although numerous research studies on coding and visual displays have

been completed, they have not been applied to the use of safety signs in workplaces. In some cases, such as new applications of energy-efficient light

sources, the research base Itself is minimal.

There is, consequently, a great need to develop criteria for safety signs and

displays. These criteria should address the following ideas:

a) Color selection, under normal and adverse conditions. Including

various types of artificial lighting, such as metal halide, sodium,

mercury, and fluorescent. The high intensity discharge sources,

which can have poor color rendering characteristics, are gaining wide

use in industrial settings due to their lower operating costs,

b) The use of retroref lective or fluorescent colors.

c) The readability of the display and the appropriate viewing distance.

d) The durability of the display.

e) Symbol recognition, legibility, and conspicuity.

f) Characteristics of luminous displays, including intensity, flash rate,

color, etc,

g) Human visual sensitivity, including color deficiencies and other

handicaps.

1.2.3 Measurement of Compliance

Although CO lor /legend requirements are liberally sprinkled through OSHA (and

other Federal agency) regulations and standards, there are few specifications

for determining compliance. Is the color the correct hue, value, and chroma?

5
Is the light source intensity adequate, and the right spectral distribution

for maximizing the legibility of the signs? Is the viewing distance and

height adequate? Is the sign size adequate for the conditions? Does the sign

provide the information necessary for employee safety? Answers to these and

other questions are needed to provide a scientific basis for specifying

requirements for any new standards or guidelines for safety and hazard markings,

as well as for determining compliance procedures.

The present report addresses the general topic of visual requirements for

safety, with a focus upon sign color and legibility, particularly under different illuminants. It presents the results from a study on safety color appearance under five different light sources, including data on the recognizabillty

of retroref lective and fluorescent colors, and provides some recommendations

for sign and color applications in workplaces.

6
2. VISUAL REQUIREI4ENTS FOR SAFETY COMMUNICATION

2.1 BACKGROUND

A worker who moves around an industrial facility must be constantly aware of

potential hazards in this environment. In general, there are three stages in

the perception and reaction of people to workplace hazards. These include:

1) Awareness of the hazard

2) Recognition of the nature of the hazard

3) Response to the hazard.

Usually (but not always) stage 1 requires performance of a visual task by the

employee. The most common visual task is the location and identification of a safety or warning sign (in addition to locating and identifying a potential

hazard). Therefore, to alert a person to a potential hazard or safety message,

one should locate a safety sign such that it: 1) attracts the attention of

the person; 2) conveys information about the hazard; and 3) is located so that

the person can respond in a timely and appropriate fashion (Chaffin, Miodonski,

Stobbe, Boydstun, and Armstrong, 1978).

The ability of a sign to attract the attention of the worker assumes that the

sign is VISIBLE. The question of sign visibility requires information about

at least four sets of variables: the visual performance abilities of the observer, characteristics of the visual stimulus (or sign), characteristics of the

illumination system, and optical properties of the atmosphere. The observer

capabilities include: observer acuity, adaptation state, age, opacity of the

lens and cornea, color deficiencies, and chromatic adaptation. Sign visibility

requires knowledge of both the illumination system characteristics and those

of the sign or visual stimulus. These Include: illumination level, type and

spectral characteristics of the illumination; as well as characteristics of

the sign such as size, shape, contrast, color, location, size of letters and

symbols, stroke width, stroke width-to-helght ratio, legibility, and cleanness.

The fourth set of variables includes those related to the optical transmission

properties of the atmosphere within the line of sight, including haze, smoke,

dirt, dust, or pollution.

In the present paper, the focus will be upon the visual performance of the

observer and the properties of the visual stimulus and the illuminant. The

reader is referred to Middleton (1963) and Douglas and Booker (1977) for a further discussion of the optical properties of the atmosphere, and to Howett,

Kelly, and Pierce (1978) for a discussion of the use of flashing lights as warning devices. Visual performance of the observer will be discussed primarily

in terms of spatial resolution including measures of acuity and contrast, and

chromatic sensitivity. Similarly the properties of the visual stimulus will

be addressed in terms of legibility and color. The illumination system will

be discussed in terms of spectral transmission, color temperature, and potential

color rendering capabilities.

7
2.2 MEASURES OF SPATIAL RESOLUTION IN HUMAN VISION

What type of detail can the human eye resolve in near and distant viewing

situations? Although a person’s ability to resolve detail can be altered by

either near or far-sightedness, as well as by disease, some measures of general

human visual acuity under "normal” viewing conditions may be summarized. The

reader is referred to Thomas (1975) for a fuller discussion of these issues.

2.2.1 Specific Variables

Visual acuity, or the resolving power of the eye, is defined in terms of the

smallest detail that the eye can resolve. The stimulus used to test acuity is

usually either a black pattern on a white background or the reverse. In either

case, lightness contrast is made as great as possible. The size of the test

pattern is systematically reduced until the critical feature is just barely

resolvable. The acuity threshold is then stated in terms of the angle subtended

at the eye by the threshold critical feature. Visual acuity is defined as the

reciprocal of the threshold, when the threshold is specified in terms of minutes

of arc. Normal acuity is 1.0, corresponding to a pattern that is just barely

resolvable and whose critical dimension subtends 1 minute of arc at the eye.

Thomas (1975, p. 234) says "In Snellen notation, acuity is expressed as the

ratio of the distance in feet at which a detail is resolved to the distance at

which the detail would subtend 1 minute of arc. Thus, 20/10 indicates that a detail that is just resolved at 20 feet would subtend 1 minute of arc if viewed

from 10 feet. The equivalent decimal acuity is 2.0." There are a variety of

test patterns which are used to measure acuity. In general, the test pattern

may be one of the six following types.

2. 2. 1.1 Minimum Distinguishable

What is the smallest point, line, or other shape that can be recognized on a contrasting field? Hecht and Mintz (1939) showed that when conditions are optimized, a threshold width of 0.5 seconds of arc was obtainable for a long

dark line on a very bright background. This is more than two orders of magnitude (120 times) smaller than the traditional one-minute-of-arc acuity

threshold, and was made possible by the great length of the line, and even

more by the extreme contrast obtainable with an opaque object viewed against a self-luminous background. Much lower contrasts are achievable on painted

signs, and the threshold in such a "real-world" situation is considerably

larger.

2. 2. 1.2 Minimum Separable

This task is usually tested with two dark points or lines whose distance apart

is gradually changed. The smallest distance between the two targets in which

they are resolved individually is the measure of interest. Craik (1939) found

that under ideal conditions, 0.5 minute of arc was the minimum separable gap that was resolvable.

8
2.2.

1.3

Vernier Acuity

Vernier acuity may be defined as the ability to discriminate the break between

two end-to-end lines that are slightly displaced laterally. Berry (1948)

showed that such thresholds range down to 1 to 2 seconds of arc. Vernier

acuity Is not usually relevant to sign visibility.

2. 2. 1.4 Minimum Recognizable

This measure of visual acuity applies to the recognition of distinct shapes

such as Landolt rings or Snellen letters. A Landolt ring consists of a black

circle with one gap located at varying positions, similar to a letter "C". The

ring Is varied In size, maintaining strict proportions, to find the smallest

gap that can be seen. Snellen letters are alphabetic characters which are reduced In size until they are barely legible. Threshold for this task (minimum

recognizable) Is based on stroke width, length of the letter arms, and width

of gap between arms (Sloan, 1951).

2. 2. 1.5 Contrast Sensitivity

Another way of assessing the resolving power of the visual system. Is by

determining the minimum contrast needed to see a grating pattern (Schade, 1956).

The word "grating" refers to a pattern of alternating light and dark bars. By

reducing the difference In luminance between the light and dark bars, a "contrast" threshold may be obtained. The reciprocal of threshold Is termed "contrast sensitivity". One common definition of contrast particularly as applied

to gratings Is the following;

C * (L max - L min) / (L max + L min)

where:

C = contrast

L max = luminance of bright bars

L min = luminance of dark bars

This definition of contrast Is also referred to as "modulation".

The number of light and dark bars (cycles) per degree of visual angle describes

the fineness of the grating. Campbell and Robson (1968) provided Illustrative

data showing the contrast sensitivity versus spatial frequency for square and

sine-wave gratings at two luminance levels.

2.2.2 Variables Affecting Resolution

The variables which affect a person's ability to resolve detail can be divided

roughly Into six categories: Illumination level (luminance), retinal location,

pupil size, spectral composition of the lllumlnant, orientation, and viewing

distance. The effect of these different variables will be discussed to determine

their Impact on visual resolution.

9
2. 2.

2.1

Illumination Level

Acuity in general depends on the luminance of the background against which the

dark target is seen (or the target luminance, if it is the background that is

dark). In the practical case of reflecting signs, the dark portions of the

display have measurable luminance, and that luminance is also relevant.

Generally, acuity increases with illumination level and is better at photopic,

rather than scotopic levels of illuminantlon. The photopic luminance range

begins at about 1 footlambert (fl), with good color discrimination occuring at

levels above this.

2. 2. 2. 2 Retinal Location

Many researchers (Ludvigh, 1941; Mandelbaum and Sloan, 1947; Sloan, 1968) have

shown that acuity is optimal when the target is viewed by the central fovea of

the eye. In the periphery, acuity increases slowly as the intensity of the

illumination is increased. Under semi-dark (scotopic) conditions, when the

rods mediate resolution, acuity is highest for targets at 4 degrees eccentricity

(4 degrees from the central fovea, Mandelbaum and Sloan, 1947). Apparently,

there is little relation between the distribution of the rods and scotopic

acuity, as the greatest concentration of the rods is at about 20 degrees

eccentricity. Maximum scotopic acuity may be as much as 10 times less than

maximum photopic acuity, however (Brown, 1965).

2. 2. 2. 3 Spectral Composition of Illumination

Of interest to visual safety requirements is the question of visual acuity

under narrow-band versus broad-band illuminants. This question does

not appear to be easily answered, since it appears to depend upon which measure

of acuity is used. Narrow band illumination reduces chromatic aberration and

might be expected to yield higher acuities. Shlaer, Smith, and Chase (1942)

found improvements with monochromatic illumination when the measure was minimum

visible acuity, while Baker (1949) found improvements when the measure was vernier acuity. However, Shlaer et al. ( 1942) found no difference between

acuities measured in narrow-band and wide-band illumination for the Landolt

ring measure of visual acuity.

Does acuity depend on particular wavelengths when narrow band illumination is

used? According to Thomas (1975), if higher intensities are used, where acuity

no longer varies as a function of intensity, and assuming a moderate pupil

diameter, acuity does not appear to vary as a function of wavelength. (For

very small pupils, where diffraction becomes the limiting factor, acuity

appears to be higher for short wavelength illumination than for longer

wavelength Illumination.)

2. 2. 2. 4 Orientation

Lines or striations that are oriented vertically or horizontally are seen better

than lines which are oblique (Ogilvie and Taylor, 1958; Higgins and Stultz,

1948; Shlaer, 1937; Campbell, Kulikowski and Levison, 1966; and Watanabe, Mori,

Nagata, and Hiwatashi, 1968).

10
2. 2. 2. 5 Viewing Distance

As the viewing distance of the target changes, the lens of the eye changes

shape, or acconuaodates, in order to focus on the target. In general, all eyes

have a near point limit, such that signs or objects presented closer than the

"near-point” cannot be brought into sharp focus. As a person ages, the eye

steadily loses its ability to focus for near work; in other words, the near

point recedes. In most people, the need for bifocals or reading glasses to

overcome this loss is felt about age 40 to 50. Myopic (near sighted) eyes

also have a "far point" focus for which targets presented beyond this point

cannot be sharply resolved. Acuity suffers if the target is outside this

resolvable range.

The reader is referred to Howett (1983) for a more complete discussion of a methodology for calculating legibility from visual acuity. Suffice it to say

for the present paper, that Smith (1979) recommends a minimum letter height

for 100 percent legibility of about 0.84 in. for a viewing distance of 10 ft

and 2.1 in. height at 25 ft, or a letter height which subtends about 10 to 24

minutes of arc. No comparable recommendations exist for symbol size. The

Howett paper provides a means of calculating letter size for observers with

different visual acuities.

2.3 COLOR SENSITIVITY AND COLOR CODING

The ability of the human eye and brain to distinguish the color of objects is

known as color vision (or chromatic visual perception). Not all people have

normal color vision and the specification of safety colors should take this

fact into consideration. Color vision defects will be discussed further in

section 2.3.1.

The International Labour Office (1972, p. 323) states that: "From the point of

view of occupational safety, colour vision is of great Importance as many

accidents are caused by lack of suitable lighting or by failure on the part of

a worker to identify conventional identification colours, such as on electric

cables, gas cylinders, pipelines, guide marks, control buttons of machines,

safety devices, and limit signals."

The concept of the color of an object is not as simple as it might appear at

first. In general terms, the color appearance of an object depends on three

main variables:

A. The visual sensitivity of the observer at the moment the object is

viewed;

B. The spectral reflectance (or transmittance) distribution of the object,

dependent on the particular pigments or dyes that give the object its

color; and

C. The type of illumination under which the object is viewed.

11
2.3.1 Color Sensitivity

Human visual sensitivity is mediated by two primary types of photoreceptors,

the rods and the cones. The rods, which are located outside the center of the

eye (central fovea) are extremely sensitive to light, being capable of detecting the presence of only one or two quanta of light (Cornsweet, 1970). They

are, however, insensitive to color. The cones, on the other hand, are maximally sensitive to color and color differences. There are three cone pigments, with maximal sensitivities occurring at about 450 nm, 530 nm, and

560 nm (Hurvich, 1981).

In the United States (and Europe) about 8 to 10 percent of adult males

(Caucasian) and 0.5 percent of adult females (Caucasian) are color defective,

with variations in these percentages depending on the ethnic population studied

(Rubin and Walls, 1969; Krill, 1972). There does appear to be some variation

in the incidence of color defects in different countries and different ethnic

populations, although such variation will not be discussed in detail here.

Such persons may simply be missing one or more of the three photopigments, or they may possess an anomalous pigment. Thus, dichromatic observers have only

two pigments, while a cone monochromat (extremely rare) only has one. A rod

monochromat, also an extremely rare individual, has only the rod mechanism

active so that both visual acuity and color sensitivity are drastically reduced

(Hecht, Shlaer, Smith, Haig, and Peskin, 1948). The various dichromatic deficiencies are of particular concern in the workplace, however. Commonly occurring dichromatic defects are related to the absence of the red photopigment

(protanopia) or the absence of the green photopigment (deuteranopia) (Vos and

Walraven, 1970). The third, much rarer, type, tritanopia, is related to the

absence of the blue photopigment. In addition to the loss of photopigments,

another class of color defects—the most common type—is the anomaly, in which

the person is still trichromatic, but the spectral sensitivity of one photopigment is shifted from the normal. Persons with these anomalies will perceive

colors somewhat differently from the normal and discriminate colors somewhat

more poorly.

Both protonomalous and deuteranomalous defects are generally more common than

the comparable dichromatic defect (Rubin and Walls, 1969). Rubin and Walls

(1969) give the following breakdown for the estimated 8.8 percent of the male

population that is believed to be color deficient: 5 percent deuteranomaly;

1.3 percent protanomaly; 0.0001 percent tritanomaly; 1.2 percent protanopia;

1.3 percent deuteranopia; and 0.0001 percent tritanopia. Although tritanopic

defects are extremely rare, (and occur equally among males and females),

acquired color defects in which sensitivity to blue is lost (due to injury or disease) are more common. In addition, as one ages, one's lens and cornea

yellow, thus reducing sensitivity to blue. Eye diseases such as cataracts and

glaucoma also reduce sensitivity to blue. Lakowski (1969) estimated the

percentage of acquired color defects to be about 5 percent of the population.

The practical effect of color deficiency is to cause observers to make abnormal

color matches or confusions between colors. Because both major types of

defects—protan (Including protanopia and protanomally) and deutan (including

deuteranopia and deuteranomally) —are concentrated in the red and green.

12
confusions between these colors must be carefully considered. Blue-yellow

confusions are rare, so that it is not economically practical to make any

allowance for them in designing color codes. Work cited by Judd (1948) suggested that a red should be somewhat orange, while a green should be somewhat

blue to reduce confusions by protans and deutans. The current standard colors

for traffic light signals reflect this concern.

Dichromats, unlike trichromats, only require two primary colors to match any

third color. As a result, they will see as identical entire ranges of colors

that appear quite distinct to a trichromat (see figure 1). For example,

protanopes (figure la) confuse reds and bluish-greens, deuteranopes (figure lb) confuse purples with pure greenish-blues, and tritanopes (figure Ic)

confuse blues and greens. Both full-fledged protanopes and deuteranopes appear

to lack totally the perceptions that color-normal observers term red and green;

they see the world only in blues and yellows (Judd, 1948, 1949). (This conclusion can never be certain, but is widely accepted as highly probable.)

Tritanopes appear to have better overall color discrimination with defects in

wavelength discrimination emerging only in the blue-green region (Smith, 1973).

They are believed to see the world entirely in reds and greens. (It should be

noted that color defective observers often can distinguish colors on the basis

of luminance cues .

)

As is seen in figure 1, the CIE chromaticity diagram (to be explained in

greater detail in section 2.3.3) can be used to define the confusion lines for

dichromats because the colors which appear to be the same to a particular type

of dichromat all lie on a straight line radiating from a single point (Fry,

1944). This point is different for each type of dichromat. In addition to

color confusions, brightness perceptions may also differ from normal in those

with color defects. The most drastic change is that reds become very dark for

protanopic and protanomalous observers.

One important aspect of the abnormal color perceptions of anomalous trichromats

can be measured by the use of an anomaloscope, an Instrument in which pure

yellow light is matched by a mixture of red and green. The proportion of red

to green needed for a match with yellow indicates whether the observer is

"red-weak" (protanomalous), "green-weak" (deuteranomalous) , or color-normal.

Anomalous trichromats require three primaries to match a given color, but use different proportions than would a normal trichromat (Brindley, 1970).

Thus, for example, pure yellow is seen at about 578.3 nm for a deuteranomal

,

583 for a protanomal, and 576 nm for a color normal observer (Linksz and Waaler,

1968). While the color confusions of anomalous observers are somewhat similar

to those of the corresponding class of dichromats, they do not involve the

confusion of entire lines of color in the chromaticity diagram, as is found

with dichromatic observers. Because of their prevalance, color confusions

should be considered in designing a system of safety colors for populations

not selected for normal color vision. In fact, because the common screening

devices for color-vision defects are very far from fully effective in detecting

anomalous trichomats, it is desirable to allow for red-green confusions even

for populations thought to be screened for normality. Bailey (1965) suggests

that such tests may pass as many as 75 percent of color-anomalous observers,

for example.

13
Figure la. Protanopic chromaticity

confusions shown on the

(x,y) chromaticity diagram

Figure lb. Deuteranopic chromaticity

confusions shown on the

(x,y) chromaticity

diagram

Figure Ic. Tritanopic chromaticity

confusions shown on the

(x,y) chromaticity diagram

Figure 1, Confusion lines of dichromats

Figures reproduced from Judd and Wyszecki,

Color in Business, Science, and Industry , Second Edition, (1963) with permission of

John Wiley and Sons, New York,

14
2.3.2 Visual Adaptation

In addition to the physiological defects in color vision that have already

been discussed, there are also normal moment-to-moment variations in visual

sensitivity as a result of adaptation to different light sources. Three kinds

of adaptation occur—light adaptation, in which the eye's sensitivity

decreases rather quickly following a change to a higher level of illumination;

dark adaptation, in which the sensitivity increases more slowly following a change to a lower level; and chromatic adaptation, in which the chromatic

sensitivity of the eye shifts with a change in the color of the light source. Dark adaptation occurs when an observer goes from a brightly lit area, such as outside, to a dimly lit interior space. Depending on the darkness of the

second space, a finite period of time, from 1 to 30 minutes, is required to

attain the new higher level of visual sensitivity. During this time, because

the scene being viewed is so much dimmer, the person can lose the ability to

perceive objects and colors, until the eye adapts to the new luminance level.

The reverse process of light adaptation, occurs much more rapidly—on the

order of 1 to 2 minutes (Cornsweet, 1970). During this very brief transition,

a person can be temporarily blinded, as happens when leaving a darkened theater

on a sunlit day.

Chromatic adaptation occurs when a person spends time exposed to a light source

of a particular color. When the person moves to an area lit by a different

source, chromatic sensitivity will be altered progressively as the eye readapts

(Hurvich, 1981). By way of illustration, suppose the initial light source is

not pure white, but somewhat bluish. After exposure to this light for some

time, the bluish stimulation fatigues the blue receptors of the eye proportionately more than the red or green receptors. Now suppose that the second source

is pure white in color. Although it supplies equal stimulation to all three

color receptors, it does not appear white to the blue adapted person. Rather,

it appears yellow, because the blue receptors are fatigued and respond proportionately less than the red and green receptors. (Yellow is the result of

simultaneous red and green receptor stimulation.) This result is temporary,

however, because the white light is no longer disproportionately stimulating

the blue receptors so that they recover their sensitivity, and the initially

yellow-appearing light soon appears white. Thus, the effect of the chromatic

adaptation process is to cause simultaneous changes in both sensitivity

and color perception with the net result, after adaptation is complete, being

some degree of stability in the perceived colors of objects under various

light sources.

Marked chromatic adaptation will occur to a narrow band illuminant such as low pressure sodium whose dominant wavelength of 589 nm stimulates the red

photoreceptors most strongly, the green receptors somewhat less strongly, and

the blue receptors not at all. As a result, color perception is noticeably

distorted during the first few minutes of subsequent exposure to a "white”

light. There is an Initial greenish-blue cast to everything because the blue

receptors have remained highly sensitive, while the red receptors have become

highly insensitive and the green receptors are in between.

15
2.3.3 Specification of Color Appearance

For a color to be seen as such, the light source shining on the surface must

supply light of the appropriate wavelength. Thus, a "red surface appears red

because it selectively absorbs wavelengths other than red, and it reflects

more of the long wavelengths than of those in the middle or short wavelength

end of the visible spectrum. Sources, surfaces, and media that are not differentially selective in the wavelengths they send, reflect, or transmit to the

eye are seen as ’achromatic’ rather than colored. They appear black, gray or white" (Schiff, 1980, p. 35). Note, however, that the red object cannot

preferentially reflect long wavelengths if no long wavelengths are supplied by

the light source. The worst type of light source for general illumination is a monochromatic (one wavelength) source; no object, regardless of its reflectance spectrum, can send any light to the observer’s eye other than that one wavelength, since no other wavelength is there to reflect. Consequently, use

of a monochromatic light will drastically alter the appearance of a colored

object compared with "white" light. To deal with the problem of the way in

which a light source can alter the perception of color, the CIE (1974) developed

a Color Rendering Index (CRI) for specifying the color rendering properties of

a light source. The lES (1981, p. 1-8) defines color rendering as "the effect

of a light source on the color appearance of objects in conscious or subconscious comparison with their color appearance under a reference light source."

The Color Rendering Index provides a "measure of the degree of color shift

objects undergo when illuminated by the light source as compared with the

color of the same objects when illuminated by a reference source of comparable

color temperature" (lES, 1981, p. 1-8). The lES mentions that the CRI does

not yet completely account for chromatic adaptation or color constancy, but

that it does provide an agreed-upon means of comparing lamps for color

rendition.

Specification of exactly what is meant when one gives a name such as "red" to

a color even under ordinary daylight is not easily done. Does one mean "red",

"magenta", "pink", or "burgundy"? How can one specify "red" so that another

person can understand and reproduce the intended color? To address this problem, a number of color specification systems have been developed. Major systems for specifying object colors include the Munsell system, the ISCC-NBS

color names, and the CIE Chromaticity diagram. Each will be discussed briefly

in turn.

The Munsell color system organizes a set of 1600 color chips into a threedimensional solid. Hurvlch (1981, p. 275) describes it this way; "The individual chips are ordered into a three-dimensional color solid with a vertical

black-to-white axis. HUES are arranged in equal angular spacing around the

central axis and CHROMA (saturation) is the distance of a chip from the central

axis at any given VALUE (lightness) level." Specifications for particular

Munsell colors are given by three sets of alphanumeric characters which specify

hue, value, and chroma.

The ISCC-NBS system of color names is a coarser subdivision of object-color

space than the Munsell system. The ISCC-NBS system is based on the use of

simple color names, easily understood without training. The blocks in color

16
space corresponding to the ISCC-NBS color names are defined in terms of Munsell

notation. Kelly and Judd (1976) discussed the idea of a Universal Color

Language (UCL) which would include both the ISCC-NBS color naming system and

the Munsell notation system. As they summarized it, the Universal Color

Language is "a method or language of designating colors in simple, easily

understood but accurately defined color designations in definite, correlated

levels of accuracy of color designation" (p. A-18). The UCL describes six

levels of increasing color specification accuracy. In each level, the com- plete color solid is divided into specified numbers of color blocks; the boundaries for each block are defined; and each level is related to all other levels.

In level one, colors are specified in terms of 13 common color names. These

13 blocks are further subdivided into 29 blocks for level 2. Level 3 constitutes the ISCC-NBS method of designating colors, using a full set of 267 color

names. Level 4 is divided into about 1,500 blocks, corresponding to the

Munsell system. In level 5 the Munsell system is subdivided further by visual

Interpolation into even finer detail. Finally, in level 6, color is measured

instrumentally and specified numerically by the CIE chromaticity coordinate

system (to be discussed below). Thus, the UCL provides a way of systematically

defining the appearance of colors. These specifications apply only to colors

seen under average daylight or CIE source C.

Another system for specifying the color of an object or light is given in its

most familiar form by the CIE chromaticity diagram. This system is based on

the principle that three fixed colored lights (or "primaries") can be mixed to

match any color (by means of a colorimeter or other instrument). The amounts

of the three primaries needed to match the color are called tristimulus values.

To avoid variations in matches between observers, the CIE specified a "Standard

Observer", based upon the average values of a substantial number of observers

(Wyszeckl and Stiles, 1967). The color matching data of the CIE 1931 Standard

Observer are considered representative of the normal human eye. The system

is defined by three functions of wavelength, x, y, and z which represent

the tristimulus values of the single wavelengths of the spectrum. (The primaries of the CIE system were chosen in such a way that these spectral tristimulus

values are all-positive functions. Other choices of primaries can result in

negative values.) Hurvlch (1981, p.284) states: "To specify any illuminated

object or surface colorlmetrically we only require the object's or surface's

spectral reflectance or transmittance and the spectral energy distribution

(in relative terms) of the light source illuminating it. If the products of

these two distribution curves at each wavelength are then multiplied by each

of the standard observer spectral tristimulus values at each wavelength and

the resultant values for all wavelenths added separately, we obtain the three

numbers needed to specify the color. These three summed values are called the

X, Y, and Z tristimulus values." The chromaticity coordinates x, y, and z are fractional equivalents of X, Y, and Z; i.e., X = X/(X+Y+Z), etc. Because the

CIE chromaticity coordinates are fractions which sum to unity, if two coordinate

values are known, the third can be derived arithmetically. This principle has

been used to develop the CIE chromaticity diagram, which is a two-dimensional

diagram upon which the x and y coordinates are plotted (see figure 2). This

diagram can be used to plot the chromaticity of any object, thus enabling its

color to be specified without reference to a set of color chips or standard

colors

.

17
VALUES OF X

Figure 2. CIE chromaticlty diagram containing the

ANSI standard safety colors illuminated

by daylight

18
In addition to the diagram itself, figure 2 plots the chromaticity values of

the five basic ANSI standard safety colors for daylight illumination. Since

the spectral reflectance of the object, and the relative energy distribution

of the illuminant are the physical measures from which these coordinates are calculated, the accuracy of the coordinates is limited only by the accuracy of

the physical measurements. Three-decimal-place accuracy of x and y is currently

routine, and under special circumstances, the fourth place can be meaningful.

As an illustration of the three systems of color specifications discussed

above, an example can be taken from the ANSI Z53. 1-1979 Standard for Safety

Colors (ANSI, 1979). This standard specifies Safety Red by the Munsell notation

7.5R 4.0/14. The 7.5R portion indicates the specific red hue; 4,0 the Munsell

value (slightly below the medium lightness of value 5); and 14 the Munsell

chroma, a quite high saturation. The standard also gives the equivalent CIE

notation, which, to three figures, is x = 0.596, y

= 0.327, and Y(%) = 12.00.

The Y value, in the CIE system, is used to indicate the percentage luminous

reflectance of the color sample. Finally, the descriptive ISCC-NBS color name

is given by the standard as vivid red.

2.3.4 Color Coding Research

Color has been used extensively to code information (often when speed of

communication is desirable). Christ (1975) analyzed data from 42 studies to assess the effect of color coding on visual performance. He found that when

subjects were asked to identify two aspects of a visual display, such as color and shape, identification of color was more rapid and more accurate.

Color was particularly superior as the number of stimuli increased, although

it remained inferior to alphanumeric coding (perhaps the most familiar coding

dimension). Christ (1975, p. 559-560) commented that "The most clear-cut

finding is that if the color of a target is unique for that target, and if

that color is known in advance, color aids both identification and searching."

Only alphanumeric characters emerge as a superior coding dimension to color.

Use of Irrelevant colors, however, may interfere with the accuracy and speed

of identifying or locating target attributes other than color. For the purposes of workplace signage, however, Christ's review underscores the ability

of color to attract attention and encode relevant safety information in a rapid, accurate fashion. Color is particularly effective in a redundant cueing

situation where the audience is knowledgeable about the color code—as is the case with signs in workplaces. Other individual studies have reinforced the

finding that color is a particularly effective coding device. Thus, Saenz and

Riche (1974), Shontz, Trumm, and Williams (1971), and Smith and Thomas (1964),

found that color coding reduced search time and increased accuracy. This

advantage is most clear-cut if the number of colors in the code does not exceed

8 to 10 (Cahill and Carter, 1976). Another study, by Easterby and Hakiel

(1977), did not find clear evidence of the superiority of color coding. This

study, which assessed symbol recognition, found that image content, perhaps

comparable in information capacity to the alphanumeric characters discussed

earlier, was more important than color coding in determining sign recognition.

Yet, their subjects reported strong stereotypes for the use of color for fire,

poison, and caustic hazard-warning symbols, Bresnahan and Bryk (1975) reported

that industrial subjects associated red and yellow with a rated degree of

19
hazard warning, thus suggesting that sign color can aid in communicating both

the presence and level of hazard.

In summary, the preceding review of some color coding research underlines the

importance of color coding in communicating information both rapidly and

accurately. Unlike shape or size, color appears to be more effective, particularly if the code is limited to about 8 to 10 colors. Only alphanumeric

characters (and perhaps pictorial symbols) are more effective coding dimensions

than color—and this may be due to widespread familiarity with the characters.

The use of color as a known, redundant cue appears to be highly effective,

however, thus suggesting that the use of color-coded word/symbol signs is one

of the best means of communicating safety information at least in the United

States.

2.4 SIGN PERCEPTION

2.4.1 Background Research and Practice

Written signs are commonly used in industrial settings to alert workers to the

presence of hazards and to provide safety information and instructions. They

are particularly important in alerting the new worker who is unfamiliar with

the job and industrial setting. These people are at higher risk during the

initial months on the job (National Safety Council, 1979)

Recommendations about the effective use of signs assume that such messages are legible and visible in industrial settings. A number of factors may alter the

visibility of such signs, however. These include low levels of illumination,

poor contrast, poor color rendering, poor positioning, inadequate size, and

poor durability. The effectiveness of signs can also be reduced by excessive

visual clutter in the Immediate neighborhood of the signs, including the presence

of too many other signs. Even a single sign can be over-cluttered, with the

inclusion of too many words or symbols.

2.4.2 Observed Sign Use

In a document prepared for NIOSH, Lerner and Collins (1980) reported site visits

to six industrial plants to observe safety symbol, sign, and color use. Although

they dealt mainly with sign use, they also documented different industrial

uses of safety colors that are relevant to the present report. The six industrial sites studied represented a diverse range of industries, and included:

the manufacture and assembly of truck engines, ceramic glass, aircraft, ships,

as well as chemical and oil refining. These authors found that safety signs

related more to potentially serious hazards such as explosion, fire, or the

need for protective gear, with somewhat less reliance upon signs for frequently

occurring but less serious hazards (such as slips, trips, and falls). With the

exception of one site, the common practice was to use word signs, often quite

lengthy signs. Of particular interest to the present report, was the widespread use of color coding to delineate areas for special protective gear or particular hazard. For example, yellow lines were commonly used to indicate

a generally hazardous area; green to indicate the need to wear protective

equipment or the presence of a safe walkway; orange for explosives; red for

20
fire-related equipment or high hazard area. In contrast to signs, here the

color was used as the entire message with the workers having presumably learned

the meaning of the color code before entering the job site. Lemer and Collins

found that the use of yellow as a hazard warning was widespread and was used

to indicate the extent of hazardous areas; moving parts and equipment; overhead

hazards (such as cranes); and occasionally to indicate areas where personal

protective equipment was mandatory (a message sometimes coded with green, as well). These authors commented that, in some worksites, because of the extensive use of color coding, signs were infrequently used. In addition, color

coding could be more spatially precise. Indicating the exact area where certain

behaviors were expected.

Another question that Lemer and Collins addressed was the ways in which signs

were presented.

They state (1980, p. 24) that; "In other words, where are they

typically located, how are they illuminated, where are they located

with respect to the hazards they represent, and what is the background against which they are presented? Although such details are expected to vary, there were highly idiosyncratic practices and

extreme variability in sign presentation among the sites visited.

Even the same message. Eye Protection Required, was presented in

many different ways; signs were placed on stands in the aisles, or mounted on walls (sometimes well above eye level and out of the

usual visual field), or above entrance ways, or on fixtures and

equipment. Often, signs were presented in clusters, rather than

singly. Lighting varied from signs poorly placed in shadow, to ones placed in bright illumination. Warnings were placed at

entrances, sometimes located around the workspace, and other times

mounted on or near the hazard. [Warning is used generically here

to refer to the entire class of hazard warning signs, including

those for danger and caution, as well as warning.] Sometimes

warning signs were difficult to see due to clutter, poor

maintenance, or blending into the background color. (In some cases

the predominant workplace color was yellow to yellow-green, making

yellow warning signs obscure). As a result, no ’typical’ or ’representative’ contexts were Identified. What is a familiar

context in one setting appears unusual in another plant or even in

another section of the same plant due to differences, in hazards,

layout, and sign usage."

Although this study was limited to six workplaces, it did identify a number of

different industrial practices for colors and signs, and reinforced the need

to study the appearance of safety colors under different illuminants.

2.4.3 Symbol Sign Research

Symbolic signs are also used to provide Information, because, when their

meaning is known, they can be recognized more rapidly and accurately than

comparable word signs (Janda and Volk, 1934; Walker, Nicolay, and Stearns,

1965). Because symbol signs are effective in communicating information without

21
the use of a specific written language, they are used where language or literacy barriers may exist. (They can be effective only when the target

audience understands the intended meaning, however.) Both word and symbol

signs are used as a common means of warning personnel and reinforcing safe

actions. Laner and Sell (1960) determined, for example, that safety posters

using both pictures and words were effective in increasing safe behavior, even over a period of several weeks.

While the bulk of symbol research concentrated upon symbols for highway and

automotive applications, a number of studies addressed the issue of safety

symbols. Easterby, for example, conducted a series of studies on symbols for

consumer products and determined that for symbols for fire, poison and caustic

hazards, people preferred descriptive symbols to prohibitory symbols. They

also tended to prefer graphically more complex symbols to simpler, more abstract

symbols (Easterby and Hakiel, 1977). The image content of the symbol was, not

surprisingly, found to be the factor which most determined the recognizabillty

of a symbol, far more than color or overall shape coding.

Lerner and Collins (1980) and Collins and Pierman (1979) conducted several

assessments of fire-safety symbols which uncovered severe problems with

selected graphic renditions of the "exit" and "no exit" messages. At least

one "no exit" symbol was found which communicated the message of "exit" or "safe haven" more sucessfully than it did "no exit". These authors pointed

out that situations in which symbols communicate a message opposite to the

intended one are potentially very dangerous.

Collins, Lerner, and Pierman (1980) assessed the meaningfulness of 2 to 3 sets

of proposed images for 33 hazard warning and safety information messages, with

222 employees from Industrial plants in 3 separate geographical locations.

They found that understandability varied widely for different symbols, with

symbols for laser, radiation, general warning and biohazard being poorly understood. Yet, symbols for personal protective gear, first aid, prohibition, and

fire emergency were generally well understood. The understandability of the

symbol appeared to be related, at least, in part to its inclusion of a person

with the depicted hazard, action, or equipment, and in part to the pictorial

nature of many of the symbols.

This work was extended by Collins (1983) to an evaluation of symbols for 40

messages for mining applications. These two studies identified a set of symbols which successfully convey hazard warning and safety information. Problems were seen for the very abstract symbols such as radiation and biohazard,

as well as for the more representational flammable hazard symbol. Recommended

symbols based upon the results of both studies are presented in figure 3.

In the course of the project on mine-safety symbols, Collins also had about 220

miners rate the perceived hazardousness of a set of surround shapes (octagon,

diamond, triangle, inverted triangle, circle, and square) for different interior

images (poison, explosion, entanglement, general warning, and no image). The

results indicated that the diamond was ranked as most hazardous consistently,

with the octagon a very close second. The two triangles were ranked next, with

the circle and square consistently ranked as least hazardous. Because the

22
lAZAID HAXNINC SYMBOLS

Figure 3. Sjnnbols suggested for safety messages

23
ADDITIOHAL BAZARD HARHIMG SYMBOLS

CORROSION BOT SURFACE PINCH POINT

CUT/SEVER

TO BE USED ONLY AFTER TRAINING OR WITH

SUPPLEMENTARY HORD MESSAGES

RADIATION LASER

Figure 3. S3nnbols suggested for safety messages

24
PERSONAL PROTECTIVE

gear (MANDATORY ACTION)

EYE PROTECTION BARD HAT

SAFETY CLOVES SAFETY SHOES

i

MB'

EAR PROTECTION

FIRST AID

SAFETY EQUIPMENT

EYEWASH SAFETY SHOVETv

FIRE BBRCEHCY IQDIPMEMT

flKE EXmiCDlSHIA FIRE BOSE AID REEL

Figure 3 . Symbols suggested for safety messages

25
HO SMOKING

PROHIBITED ACTIONS 0 SO HOT TOUCH OPEN FLAME

EXIT

EGRESS-RELATED

DIRECTIONAL ARROW

Figure 3. Symbols suggested for safety messages

26
diamond is used by the Department of Transportation (1978) to indicate warning,

because it allows a larger interior image than the ISO-recommended triangle,

and because it was generally ranked as most hazardous, Collins (1983) suggests

that it be given further consideration as the surround shape for hazard warning.

The effectiveness of combined word and symbol signs remains to be examined.

Current sign practice typically follows the ANSI Z35 format (to the extent that

any format is used). This format uses a signal word such as Danger, Caution,

or Notice, with a short word message which describes the hazard or recommended

action. The communicative value of adding symbols to these word signs remains

to be assessed. Furthermore, the overall legibility of such combined signs

also needs to be determined.

27
3 LABORATORY STUDY OF COLOR APPEARANCE UNDER DIFFERENT LIGHTS

3.1 BACKGROUND

The preceding sections have indicated that the use of color and signs to

indicate the presence of hazards and to convey safety information in workplaces is both common and prescribed by regulation. The use of high-efficiency,

poor color-rendering light sources can markedly affect the legibility of a word or symbol message, when it reduces the contrast between the message and

its immediate background. Moreover, it can drastically alter the perceived

color of such a sign, thus nullifying the attempt to convey safety information

through color coding. Current color rendering indices do not adequately

specify the extent to which such a source would alter the perception of safety

colors. A low index value is a signal that possible color distortions should

be looked for, but this value provides little information about how colors

will be perceived and identified.

As a result NBS undertook a laboratory study to assess the extent to which

different types of light sources affect the perception of a number of colors,

including safety colors. This study was intended to define the kind and extent

of shifts in color appearance for a number of common workplace illumlnants,

including tungsten, metal halide, fluorescent, high pressure sodium, and low

pressure sodium. These light sources vary widely in color rendering index,

with none having a spectral distribution substantially equivalent to CIE

Standard llluminant C, for which the current ANSI Z53.1 (1979) safety colors were specified, or D65, the current CIE daylight standard. Consequently, it was hypothesized that some of these sources might result in a marked decrease

in the ability to Identify safety colors correctly. As a result, several

series of colors of different composition, including ordinary, fluorescent,

retroref lective, and retroref lective fluorescent, were studied under the

light sources mentioned above. (The ordinary color series included the

standard ANSI Z53.1 safety colors.)

It was hoped that the pilot laboratory study would assess the Identlf lability

of the different types of color samples under the different light sources, and

that a small set of colors could be determined which were maximally identifiable under all five sources. Such a set of colors could then be evaluated

more extensively under both laboratory and field conditions to determine their

suitability for general workplace use.

3 . 2 METHOD

3.2.1 Subjects

Seven employees of the National Bureau of Standards, three females and four

males, participated in the present study. The mean age was 37.3 with a range

of 21 to 55. All subjects had normal (20/20) or corrected-to-normal visual

acuity. They also had normal color vision, as verified by the A.O. H-R-R

Pseudo-Isochromatic Plates.

28
3.2,2 Apparatus

All experimental sessions were conducted in the Illumination Color Laboratory

which contained an 8 ft 5 in, by 6 ft 5 in. illumination chamber, with an

8 ft ceiling and removable black walls. Illumination was provided by one of

five different energy-efficient or high-color-rendering lighting systems.

These systems included low pressure sodium (LPS), high pressure sodium (HPS),

metal halide (MH) , fluorescent (FL), and incandescent tungsten (T). Table 3

presents illuminance data for each light source. Figure 4 presents spectral

power distribution data, including chromaticity and correlated color temperature, for each of the five sources. Schematic design details are given in

figure 5, with additional detail presented in appendix A.

The color samples used in this experiment consisted of four series of 5 in. by

7 in. color samples mounted in frames. The four series consisted of samples

of the ANSI safety colors (designated series 100); an additional series of

ordinary colors, intermediate between the ANSI colors (designated series 200);

retroref lective colors, some of which were also fluorescent (series 300); and

a fluorescent (non-retroref lective) series (series 400). Two samples for a number of colors from series 100 and 200 were used as controls, to determine

if color names varied within an individual sample. The total number of color

samples from all four series was 73, of which 45 were distinct colors, A

listing of each series, sample number, and color name is given in table 4.

The 100 series of colors were the central or standard colors as specified by

ANSI Z53.1 (1979), The 200 series consisted of a set of colors approximately

halfway between the standard ANSI (chromatic) colors, plus a set of experimental red colors formed by various mixtures of different red pigments. The 300

series consisted of some samples of conventional retroref lective color material

such as is used on highway signs, plus some samples of a new type of material

that is both fluorescent and retroref lective. The 400 series of colors con- sisted of regular fluorescent paints of the sort used in "black-light" displays

3.2.3 Procedure

Experimental sessions began with a 15, 30, 45, or 60 minute adaptation period

to one of the following light sources; low pressure sodium with 1 (low) or 3

(high) lamps lit; high pressure sodium; tungsten; metal halide; or fluorescent.

The shortest adapting time, 15 minutes, should have been long enough to ensure

full light adaptation (typically believed to occur in about 1 to 2 minutes;

Cornsweet, 1970), The adapting illuminance levels are given in table 3. The

lowest illuminance level, 15 fc, is well into the photopic visual range, so that color discrimination should not have been adversely affected. To avoid

influencing color judgments, the black-walled chamber was devoid of colored

objects. During the adaptation period in the illumination chamber, subjects

performed various visual tasks such as reading, writing, etc. Upon completion

of adaptation, the subject was seated 3 feet from the eye level viewing area. A black cloth was draped around the subject to ensure a color-free visual

environment.

29
Table 3. Average Horizontal and Vertical Foot-Candles for Each Light Source

Measured for a Horizontal and a Vertical Surface

Low Pressure Sodium-Low Level

Horizontal Vertical

59.75 48.04

Low Pressure Sodium-High Level

Horizontal Vertical

143.04 105.91

High Pressure Sodium

Horizontal

52.63

Vertical

43.58

Metal Halide

Horizontal

13.73

Tungsten

Horizontal

46.50

Fluorescent

Horizontal

35.54

Vertical

15.91

Vertical

32.57

Vertical

32.15

30
Table 4. Experimental Color Samples - Series 100-400

ANSI Sample Series - 100 Regular Sample Series - 200

Series Color Name Series Color Name/Composition

100/105* ANSI Purple 201/202 10 PB

110/115 ANSI Blue 203/204 10 BG

120/125 ANSI Green 205/206 5 GY

130/135 ANSI Yellow 207/208 10 YR

140/145 ANSI Orange 209/210 2.5 YR

150/155 ANSI Red 211/212 7.5 YR

160/165 ANSI Brown 213 QR-T

170/175 ANSI Black 214 QR-OP

180/185 ANSI Grey 215 QR-2

190/195 ANSI White 216 QR-4

217 QR-6

218 Safety Red

219 Bon Maroon1

220 Bon Maroon-2

221 Bon Maroon-3

222 Bon Maroon-4

223 Bon Maroon

224 Bon M & TI 02-1

225 Bon M & TI 02-2

226 Bon M & TI 02-3

Retroref lective-Fluorescent Sample Fluorescent Sample Series - 400

Series - 300

Series Color Name Series Color Name/Composition

300 R. Blue** 400 S. Yellow/S. Green

301 R. Blue-Green** 401/402 Saturn Yellow Toned W/Green

302 R.F . Green 403 S. Yellow

303 R.F . Yellow-Green 404 Orange (Mix A)

304 R. Yellow** 405 D/G Blaze Orange

305 R.F . Orange 406/407 D/G Fire Orange

306 R. Orange-Brown** 408 S. Red

307 R.F . Red-Orange 409 D/G Rocket Red

308 R. Red** 410 Rocket Red-Quinon Red 1 :

1

309 R.F . Purplish-Red 411 Rocket Red-Safety Red 2:1-1

310 R. White** 412 Rocket Red-Safety Red 1:2-2

413 Rocket Red-Safety Red 1:1**3

414 Rocket Red-Bon Maroon 1 :

1

415 Rocket Red-Bon Maroon 2:1

* Two color samples separated by a slash were identical. This duplication

includes all samples in series 100, and samples in sets 201-212, 401/402,

and 406/407.

** Retroref lective only, not fluorescent colors.

31
TUNGSTEN

i'igure 4. Spectral Power Distributions of Experimental Light Sources

32
MROWilTTS

m

SWIMI

C«

PIRIM

MROWATTS

RR

SQORRC

CS

f>tR

RM

UW-ftESSURE SODIUM

Figure 4

« JI09

f

« .4111 CCT M73SK

. Spectral Power Distributions of Experimental Light Sources

33
Rear Chamber Wall

Tungsten

Shutter 4 Shutter 1

1 Bulb- 1 BulbHPS Mercury

Shutter 5 Shutter 2

2 Bulbs - 1 BulbMercury

Off

HPS

Metal

Halide

On

Shutter 6

Subject

Shutter 3

1 Bulb- 2 BulbsHPS Mercury

Off

Metal

Halide

On

T

Color Sample

T

Movable Wall

Movable carriage with LPS and fluorescent

Figure 5a. Design details of illumination color laboratory

34
pigijirg 5b» Slcstcli of iHu.iuin.a.tion color l^borstory

35
Once the experiment began, the subject (always run individually) named the

sample's dominant color and its secondary color, if any. Each subject also

indicated the sample's lightness (light, medium, dark) on a simple threecategory scale, as well as its saturation (strong, medium, weak). Thus, a typical response to a sample that appeared to be orange with some red tint to

it might have been "orange/red, medium, medium", or a pure blue sample might

have been termed "blue, dark, strong". These j^esponses were recorded by an experimenter. (Lightness and saturation judgments were not included in the

final data analysis, because subjects could not make consistent ratings for

these two measures. More exhaustive training in the three color variables, as specified by the Munsell system, is necessary if consistent judgments of lightness and saturation are desired.)

During each experimental session, one of the five light sources provided the

illumination. Each session lasted approximately 30 minutes plus adaptation

time (typically 30 minutes also). About 50 color samples randomly drawn from

each of the four color series were presented during each experimental session.

Although samples were available for all safety colors, the experimental presentations concentrated on red and orange samples, from the 100, 300, and 400

series, because of the need to find a "red" perceived as red—the color used

to symbolize the highest degree of danger—under all light sources, including

LPS.

In all, a total of 116 experimental sessions were held, with a total of 5760

sample presentations. (Fewer sessions were conducted with the 200 series

because of the experimental nature of this set of samples.) The greatest number

of sessions per sample (51) was conducted under low pressure sodium, since

this light source results in the greatest color distortion. Twenty four sessions per sample were conducted under high pressure sodium; fifteen under

tungsten; thirteen under metal halide, and thirteen under fluorescent light.

36
4. RESULTS

4.1 FREQUENCY DISTRIBUTIONS

The color naming responses were tabulated and analyzed by a series of computerized data acquisition and manipulation programs. For the purpose of the present

report, color-name frequencies for each color sample were totaled (collapsed)

across subjects, adaptation periods, and illumination levels, since preliminary

inspection of the data revealed no differences due to these variables.

Tables 5 to 8 present a frequency distribution of the number of times that a particular sample was given one of twelve color names under each of the five

light sources. Decimal fractions of the total are also given, following the

frequency counts, in each column. These color names included the five basic

safety colors—red, orange, yellow, green, and blue; the auxiliary colors

purple, brown, grey, white, and black—as well as the combination categories

of red/orange, and orange/red. To create these tables, several categories of

color names were combined together. These combinations disregarded the use of

any secondary color name. Thus, blue/green was included with blue, rather

than with green. The only exceptions to this rule were orange/red and red/

orange which were categorized separately due to the special interest in "red"

as a safety color name. In addition to being identified separately, the red/

orange responses were included in the total "Red" count, and the orange/red

responses were Included in the total "Orange" count. (Frequency data for

orange/red and red/orange only are given in parentheses.) In those few

instances, where subjects gave color names which were not standard safety

color names, these were included with the most appropriate color name. Such

combinations included olive with green, gold with yellow, pink with red, and

tan with brown.

Table 5 presents data for the 100 color series; table 6 presents data for the

200 series; table 7 presents data for the 300 series; and table 8 presents

data for the 400 series. Table 9 presents the color names that were given as secondary responses in a "blend" response, as a function of the five different

light sources.

Examination of tables 5 to 8 (frequencies) indicates the extent to which a particular sample was given one or more color names under the different light sources. For the 100 series (table 5), purple, blue, and green (samples 100

to 125) were generally correctly identifed under all light sources, except

LPS. Under this source, these samples were typically identified as brown or gray. An exception to this generality is that green was frequently termed

blue under HPS. (Note that samples ending in five were duplicates in the 100

series). The yellow sample (130/135) was correctly identified under all light sources. Orange (140/145) was termed orange only under tungsten and fluorescent

lights, both orange and yellow under metal halide and HPS, and only yellow

under LPS. The red color sample (150/155) caused considerable confusion under

all light sources including tungsten. It was termed yellow or brown under

LPS, orange under HPS, and more often orange than red for metal halide. Under

fluorescent and tungsten lights, it was called red more often than orange.

37
Table

5.

Color

Frequency

Charts*

^ 00 00 <n ^

vC ^ sO 00

CM ^ CM ^ 00

CO ^

H 0

1

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hJS

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Oi

CM O O O 0\ O• • • • o ^ ^ till CM CO 00 ^

00 o o o 00 o o o • • • • ^0till 00 vO CO o>

vOo

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1 CM

o

o

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o o o o

o o o

lilt CM fN» ^ CO

CO o o o o

0 o o • • • • • o ^ f>H

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CM O O • • • • o o o o till 00 CM ^

sOO

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to H

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eu Oi hJ X

i-j fa H o

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to toX

1-3 to

38

The

first

number

refers

to

the

frequency;

the

second

to

the

percentage

of

total

responses

for

each

individual

sample.
Table

5.

(Continued)

fo in vo to^ooo ^ M ^ ^ ^91 CD o ^

•n ^ •“ o m 00 r» CD so in <N »•

fO ^ ^ ^

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^ r* ^ CM

I I »“ r>

\O

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1

r* o so ^

^ so o os till «n so so e

I I t CM in 00

o os

00 m o

• • • 0 e o

1 I I <n so ^

o o so o o

o o 00 e o

I I I I I fo m so so

cn

^ ^ o ^

I I I I I so ^ O os o fM ^ ^

o 00 e ^ OS 0 r* ^ ^ o

«- o o e o

1 I I I I os ^ ^ ^ m ••

o m in os 0 m r> CM

• • • • ^ o o o

1 I I I O 00 so CM

^ 00 « o • • 0 o

1 I so ^

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3%£ia

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^ o

H r*S S o

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u irt a m

S <7 S ^

39

LPS

1-0.03

13-0.42

1-0.03

10-0.32

6-0.19

HPS

10-0.83

(1-0.08)

2-0.17

MH

1-0.17

3-0.50

(1-0.17)

(1-0.17)

2-0.33

FL

2-0.16

(2-0.16)

(2-0.16)

10-0.83

T

1-0.08

4-0.33

(2-0.17)

(3-0.25)

7-0.58
Table

5

.

(Continued)

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m o 00 GO 00

• • • • • 0^000 I I I I I r** fo m m

00 rn VO o o ^ r* vO vO o • • • • • 0 o o o ^

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vO CM O O O

m O' o o o 0 o ^ ^ ^

1 I I I I ^ o 00 00

fO O' o o

cn 00 00 o o • • • • • 0 o o ^ ^

1 I I I I o in CO O' cn

0 o ^ ^

1 I I I I CO CM 't CO

CO o o o

CO in o GO o • • • • • 0 0 ^ 0 ^

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0

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0

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I I ^ CM

CO CO

04 0l ^ as b &4

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04 Ol ^ s

S

in

10

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ta m

(U (U

iJ s u

o

aic

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04 04

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04 04

>J X

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< in K 00 o r40
Table

5.

(Continued)

CM pH oo

J

o o

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<30 I I

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• • ' L vo fn vo

wo

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b3H

C/5 CO

fa H

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41
Table

6.

Color

Frequency

Charts

^ o IN. vo n t^9\cn^(n soorN^^u^ ^noo^^ONiA so -h in ^a n m <a in vo a

8

? ?cs

(0

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lA

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vOO

0

1

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1

lA

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0

1

SD IN

00 O

o d

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• • 0 o

1 I fO

O O O CO O 0 00 o ^ ^ ^ O

1 I I I I in <*i A m A

soo

0

1

PO o o o

OS O O O • • • • Q ^ Till •» os <0 CM

CA O O O

o• • • • O -M

I I I I flO lA lA <A

O sO vO O 0\ 00 vO o

0 o o ^

1 I I I vO <A

O O O O

0 o m o • • i • »H O ^

1 I I I Ch fO fs CA

CA

CAd

Cvj

CQ

'N. u

3

Vi CO

td3

CQ >v

(d

id&

3 O

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olA0

1 CM

cs

J

u

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o o o o

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o o o o

o o o o

I I I 00 >0 OS

CO CO 3 ^

d

H 33 .J

Cm H

•-3 O

A cs

Cd sO S o

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42

YELLOW/ORANGE

207
a

A

A

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o o A A in

CH A ^ A in A A A A C4 A ^ <n A A in m <n «scs

X

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43

13-0.87

(4-0.27)

(2-0.23)

2-0.13 5-1.00

1-0.17

(1-0.17)

5-0.83 5-1.00
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44

MAROON 221

LPS

19-0,76

2-0.08

4-0.17

HPS

(1-0.09)

11-1.00
Tabl«

6*

(ContlniMd)

0k 0) CD n <0 • CD tft ^ ^ ^ ^ ^ M ® n

n ® m r> m

I lA

§

IM

e

II

c

e

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e e e e e 5 5

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M p lA

• • e p

1 1 <n

••

p e lA r* p p p

e e e p p p p p • • • • • • • • e p o »- p p

1 1 1 1 1 1 1 1 P p ^ p ^ p M P

e

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• • • • e e «- e

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Si£i3 .

J;

Slsii

e

Use.

Z m

SSi M

^n ®

Z kO 8 P!

45

0.20

4-0.80
(Olive)

(Gold)

(Pink)

(Tan)

BLUE

PURPLE

GREEN

YELLOW

ORANGE

0/RED

RED/0

RED

BROWN

BLACK

GRAY

WHITE

^ fo fo in ^ (N ^ ^ 5

^ m n m

^ es ^ ^

CO o <N »- m

^ ^ ^ ^ ^

in

0

1

o

in 0 o

1 I m ^

0

1 m

o e o o

o o o o

I I I I I ON m ro <n m

<S CM ^ ^

<n

r* CM 01 ^ m 00 • • • • o

O O O I

I I I ^

O' CO O' ^

p** m ^ o

<n r- fO ^ 0 o o o o

1 I I t t CM r* CM m

o CM m o

0 O' €0 o 00

• • • • • ^00^0 1 • I t I r«- CM T- fo fo CM ^ ^

00 r* fo O' r*** O' CO m o o • • • • • 0 o o o o

1 I I I I p*. p*. ^ IP* «-

o o o

o o till CM CO CO ^

P- ^ o

I I I I CO <o CO.tf M ^ P* *-

CO tn O' o

Ip 00 vO lO o e o o

CM ^ O' O'

o o o o o

CO o o o o

u

D

A CO

o< ou 3 X

oo

O' o

so in

• « o o

•0.07

in ^ CM

CO ^

1 r" g

Si

t*

uO

u

LPS HPS MH eh g

to to

Oi cu S S iJ s s lu Eh

K

§

to to

0) Oi a X

to to

0< 0< B

X S

>4h Pi 3-

0 S

CMo

CO CO

46

ORANGE/BROWN

306
Table

7.

(Continued)

^ fO CO

C4 *-4 **4 CM cn <n <n <o <n fo «»» >» 9 cn CM CM m

z ^ ^ ^ <9 CM PM ^ pM ^ ^ ^ «p4 ^

eo CO CM o cn S O ^ «n »n H • • • • • M9ES f

0 o o o 1 1 1 1 s

1 1 1 00 m 9 00

p"4 A O O fv

CM O PM m «A «9

• • • • • • s 01 0 o o o o

w 1 1 1 1 1 i CM

1 1 1 1 1 cn ^

BLACK

CM CM -9 z o o 5 • • • s

A

o

<!, ??pM ^

CM A •«« A » cn CM cn O Q pm o

m Q oi p-i cn o O ^ p^ o\ « o

P • • • • • • • • • • • • • • 1 0 o o o o

1 1 1 1 1 ^ ^ ^

o o o p • 1 1 T <n CM o

0 O M O

1 1 1 1 1 <o >o *n *e

•4 pM «M PM

/"> i»p^ ^ ^^ ^ ^<PN yp^ «H 00 ^ lA A «A O O O -« 9i m r** o ^ ^ <o o o O • • • • • • • • t • • § 0 o o o 1 1 1 1 ???? ^ ^ CM 0 o1 1 o

S Sf ^4^ cSl CM pM w www W W w w w

yp\ y-v

y-N ^ ^ ^ CO o ^ CM o cn o o o • • • • • • • • •

'>«» ?? ?? ?? ? ?? o p"* «n ^ PM CM PM w w w ww w ww

CM cn o\ CM cn CM vo 9 cn

00 O CM Q O

9 cn

OO 1^ A A 9^ o u • • • • • • • • • • • • o p O O O

• Till 9\ 0> CM cn o o o o o o o

3

1 1 rs. fM1 PM

l«) ^ ^ PM in o

OO *M 9 pM 3 CM cn O 9k

• • • • 3 0 o 1 1 ?

O

cn ^ cn CM p PM •9

s o

d S 1 u CM

00 a o

d1 3 pM

0.

U

3

•Jn

CO CO CO CO CO CO CO CO o aass^H aas 0j

bh H u a a sS fa H

o

o

Q « u S O 9k M O

M O

S PM S m S <*) 5 cn 5 cn

47
Table

8.

Color

Frequency

Charts

00 <n CM m CN ^ ^ ^

00 CM cn lA ^ ^

O CO <A to to CM ^ ^

nO ^ CO CO to

CM ^ ^ ^

ON ^ CO <0 lO ^ CM ^ ^

0

1 'O'

'Oo

0

1 CM

CMO

O

I

I

o 0

1 ON 01 00

o

fQ

0

1 CM O

I ON

0

1

u

0> COoo

Qu

0^

00o00o

0

1

o sO tn O O OO 00 OO O 00 CM -H 00 o O CM o tn NO O lA o O 00 so NO so ON o O ON 00

• • • • • • • • • • • O1 01 01 O1 01 o O1 o ^ o o o o o ^ o o

00

1 NO1 CM1 sD1 sO1 On

1 ^4

1 00 i i 00 CO •A

1 CO CM

1 CO

CM CM tn CM ^4 CM

to o o

CM 00 to

• • • • o o o o till to 'O ON

O O CM O

0 ON o • • • • ^ o

1 I I I 'O CO CM to

OI ^ ^

CM O CM CM O

O O ON ON

• • • • • 0*^00^ I I I I I *-• -O CM lO

CM iM ^

CM 00 ^ CO

-M CO CO CO

• • • • 0 o o o

1 I I I CO to to

04

0^

Oi

00 z z z

u b] u

u

s o2 X

o o o CO CO ^ CO to 3 ou a« 3S

1-3 3 n. & sC bJ 3

o X 23 H O iJ S 3S b H o

.J

nJ o J -1 •J CM o b] O u o

00o

0

1

>» -4* Mf

W CO

b. H

3s

nJ CO u o >< •4'

CO CO

tx H

48

LPS

1-0.02

39-0.80

(9-0.18)

(2-0.04)

9-0.18

HPS

20-0.83

(5-0.21)

(3-0.12)

4-0.17

MH

2-0.15

10-0.77

1-0.08

FL

12-0.92

(3-0.23)

(1-0.08)

1-0.08

T

12-0.80

(2-0.13)

(3-0.20)

3-0.20
lA ^ C4 ^ 5

«A M «A

t>t m4

00 M cn (A m *9 ^ ^ ^ Q ^ <A <A m ^ r^i ^ .i« «i4 ^ <n <n m lA ^ c*^ ^ ^ ^

O ^ <n r> lA lA <N ^

>«u

s

aa

«n o eo -* «n

oe <A A m <n

• • • • • o o o o o

d>Xrl<VJ^

<A

fNk GO ^ O r«a <0 lA ^ • • • • • <p<p<j,oo

f% ^ ^ >4> fn

r*» CM lA m «D IM ^ 00 Ak

• • • • • ????? ^ CM CA

CD lA ^ ^

oo ^

a<f4cff ^ ^ o

Ak CM 1^ O fK »A ^ r^ ^ • • • • 0 O O O

1 I I I lA CM O fA ^ ^

s

O OO CM <A CM ^ 0\ OO vO o o o o o

I I j T

CM O 00

sO CM CM U-l O ^ ^ vO 00 vO

• • • • • 0 o o o o

1 I I I 1 00 CA 00 ^ ^

§w

00

«!

o

o

sg

a

lA lA Ak lA O (A CM *ii4 li^ CM

• • • • • 0 0 0 9 0

1 I T I I ^ CM CM CA

«-4 Ak lA 00 CM

«4 CM CA CM

• • • • • ????? m •» «*» <n

<n lA m r^

«s ro ts n CM

• • • • • o o e o o

r*k Pi4 r%

M4 ^ *4 ^ O • • • • •

CD CM %0

CM CM «A

pH CA <A CM

• • • • • ????? <® fM CM ^ SS• • ss• • 22 ‘f*'? ^ CM pH «4

HO ^ 00 O CM CM O CA CM

• • • • • ????? CM irt -» >» m

CM CM m m o

O ^ >M CM

• • • t • ????? -4 CA CM CM CA

^ O O 00 CA

CM CA O «M

• • • • •

<•) ????? t*« >4 CM « oi ??00 «n

OO o

O CM

• • o o• I -M CO

CO o m f'. cn

CM CO CM CM

• • • • • 0 o o o o

1 I I I I •M r*» cn CM «n

0 o

1 I p«. *«

00 00 o o

0 o

1 I

CM -a- 00 00 c*i o o o o cn

• • • • • 0 o o o o

1 I I I I ^4 ^ lA

CA CA 00 CA O CA CM O • • • • • 0 p o o o

1 T I I I CM 00 CO -H CM

«H

3

O CM » CM

•« m •» p « • • « • • oo<j>oo

00 CM <n A o

(*> Ot CM o CM (*l <9 in cO

t « • • • p o o o o

fM <») « m CM O -M CM

• • • • • o p O p O

CM lA lA pH CA

•K CM PH CA CA

• • • • • O O p o o

CM >o in

91 cn cp cn o CM ^ O CM >9

• • • • • p o o o o

O CM GO 00

>P lA O *H CA

• • • • • ?

o p O O

I T • I os CM pH CM lA

CM PH

00 00 iA O 00 00 CA pH

• • • • • O O O O O

t I i I 1 CM pH iA CM ^ CM

a

CMO

2

(O (O M (A

In H k« H

M V% h HM M W M

m H EB4 H

CO CO as

3

a 00 as ifQ >1 a:? a CM

49
Table

8.

(Continued)

o m < CO CO CO m 00 CM CO CO m

z «*4 ^ CM —H H ^ CM -H —H —

H

GOO

HM O1 §

1

«O

A

CM z O O « Q o o

1 1 flQ *-< CO

00 o> r- cn r*«. CO O O CO o o o o —^ ro r> oo m 00 00 O O 00 Cn O O o o

Q • • • • • • • • • • • • • • • S 0 o o o o 1 1 1 1 1 0 o1 1 i -H o1 1 III ^4 —

H

1 1

1 1 I 1 1 ^ ON O O 00 111 ^ ON ro

1 1 CO CO III in CM CO1 1 CO m ^4 CO CM

/->, y-s y—V y-N y-> y-N y-s y-\ y-s y-\ y-s ^ m 00 CO ^ o m

O O ^ CM o ^4 * o ^ o , o • • • • • • o • • • a o o o o o O 1 o o o o

1 1 1 1 1 1 1 1 1 S CM cn ^ CM vO m Say N«y Sm/ s-y s-y N«iy s«y s«y

y-N y^ y-s y^ y*^ y^ y-s y-s 00 CO cn ^ CM ON PN. CM Q o CM CM o o o O • • • • • • • • s o o o o o o o o —

.

III 1 1 1 o ^ CO cn CO -H CM -«4 "w* S«y w >-<y N-y w s^y

CM ^ CO 00 CO »-H ps. -d* u 00 sO CM o ^ —H —

H

^4 CM

CJ • • • • • • • 0 o o o o 1 1 1 1 1 0 o1 1 o O

1 1 1 1 1 ^ <r CO ^ vo

1 1 m CM o . o

3

O

1-^1 hJ

(<]

z

u

u

z

C5

z

PL«

u

z

I-] PQ

CO CO CO CO CO CO

a« 04 s 1-3 z Z S CS4 H H fc H

Q CO m

Ck3 -h -H

-5“

50
Table 9. Tabulation of Colors Included as Second Color in a Color

Blend Response

LPS

Primary Secondary

Blue Black

Purple Gray; red

Green Yellow; brown; gray

Yellow Gray; white; green; orange; brown; tan

Gold Brown; yellow

Orange Red; brown; pink; yellow; gray

Red Orange; brown; pink; black; gray; purple

Brown Gray; yellow; red; black; green; purple; gold

Black Blue; red; purple

White Yellow

Gray Black; white; brown; purple

Pink Brown; orange; red; yellow; white; magenta

Tan Yellow; orange

Olive Yellow

BPS

Primary Secondary

Blue Green; red

Purple Blue

Green Blue; yellow; brown; tan; gray

Yellow Green; orange; pink; brown; tan; white

Gold Brown

Orange Yellow; pink; brown; tan

Red Blue; purple; pink; magenta; brown; white

Brown Green; yellow; orange; red; black

Black Blue

White Purple; brown; gray

gray Violet; purple

Tan — Pink Orange; red; magenta; purple

Metal Halide

Primary Secondary

Purple Red; blue; magenta; violet

Blue Green; white

Green Yellow; Blue

Yellow Green; orange; brown

Orange Brown; pink; red

51
Table 9. (Continued)

Primary

Pink

Red

Brovm

Black

Grey

White

Primary

Purple

Blue

Green

Yellow

Orange

Pink

Red

Brown

Gray

White

Black

Primary

Blue

Purple

Green

Yellow

Orange

Red

Pink

Brown

Black

White

Metal Halide (Continued)

Secondary

Purple; red

Purple; blue; pink; magenta; brown; orange

Yellow; orange; red

Violet

Purple; violet; red

Fluorescent

Secondary

Blue; violet; pink; red; magenta

Purple; violet;^ green; red

Blue; yellow

Green; orange; brown; white

Yellow; pink; brown

Orange; red

Purple; pink; magenta; brown; white

Orange

Blue; violet

Purple; blue; red; black

Blue

Tungsten

Secondary

Green

Blue; red; pink

Blue; yellow

Green; orange

Yellow; pink; red

White; blue; purple; pink; brown; orange

Orange; purple

Orange; red

Blue (once)

Gray

52
It should be noted that the ANSI Safety Red color is, in fact, not a pure red,

as seen under the daylight illuminant for which the ANSI colors were standardized.

Rather, this red was deliberately moved slightly toward the orange to assist

people with common color defects in distinguishing it from black. Thus, orange

as a secondary response, or even as an occasional primary response, under good

color-rendering sources is understandable.

Brown (160/165) was accurately identified under all sources except LPS where

confusions with gray arose, and under HPS where some confusions with yellow

occurred. Black and gray (170/175; 180/185) were generally correctly identified except under LPS where black was termed purple or brown as well as black,

and gray was termed yellow. White (190/195) was also termed yellow under LPS,

but white under all other sources.

For the 100 series of color samples, the only color correctly identified under

all light sources was yellow (130/135). Major confusions arose for safety

red (150/155) under all lights, except fluorescent, with both orange and yellow

commonly occurring as confusions. The most dramatic—albeit anticipated—pattern

of distortion was the shift of the majority of the safety colors to yellow,

brown, or gray under LPS, thus indicating an almost total loss of information

about the ANSI standard safety colors for this source. This result is to be

expected because of the essentially monochromatic spectrum of LPS light, which

consists almost entirely of a narrow band around a wavelength of 589 nm, in

the yellow-orange region of the visible spectrum.

The data in Table 6, the 200 series, must be regarded as somewhat tentative,

due to the generally small number of times each sample was presented under the

different sources (particularly tungsten, fluorescent, and metal halide). In

addition, part of this set of samples was deliberately designed to be intermediate between the ANSI safety colors, and part to include a variety of different red pigments. Nevertheless, a few general conclusions can be drawn.

The green-yellow (205/206) was identified as green more frequently, than

Safety Green (120/125), with no blue confusions, under all light sources,

except LPS, where it was termed yellow. Yellow-orange (207/208) was not as successful as Safety Yellow, with many confusions with orange for most sources. Another yellow-red sample (209/210) elicited numerous orange responses for all

sources except LPS and HPS where a large number of yellow responses arose. Samples 211/212 (red-purple) elicited red, yellow, and purple responses depending upon the source. The remaining samples, 213-226, which consisted of different mixtures of red pigments varying in hue from orangish-red through bluishred, elicited a variety of yellow, orange or purple responses. Samples 213-218

were generally termed yellow under LPS, orange under HPS and red or orange

under the remaining sources. Of the series 219-226, sample 223 was correctly

identified under all sources except LPS where it was termed black, brown, or

blue. Samples 22A and 225 were also almost as successful. No red in the 200

series was identified as red under LPS, however, although some of these reds

were superior (with a higher frequency of correct identifications) to the

Safety Red (150/155). Again, however, the reader must be cautioned that a very small number of sample presentations was made.

53
Table 7 which contains data for the 300 series (retroref lective and

retroref lective-f luorescent) indicates that sample 300 is termed blue 80 percent

of the time under LPS and blue all the time under all other sources. Sample

300 is thus the sample most consistently identified as blue for all sources,

of the samples studied. (Series 400 contained no blue samples.) Sample 302,

green, is also quite sucessful, except for LPS where it was termed brown or gray. The other green samples (205/206; 120/125) were usually termed yellow

under LPS, thus confusing a hazard warning color with a safety information

color. This is a potentially more serious confusion than one with brown which

has no hazard connotation.

Sample 305 is one of the most successful orange colors studied, being

recognized as such 70 percent of the time under LPS, and all the time under

all other light sources. Thus, the 300 series contains samples that had a high percentage of correct identification as blue, green, or orange under all

light sources. None of the nominally red samples (307-309), however, were

particularly sucessful, with marked confusions occuring between orange and

red. In addition, the retroref lective white (310) apparently had too low a reflectance, since it elicited many confusions with gray, except under LPS

where it was seen as yellow.

Consideration of the 400 series (fluorescent colors) given in table 8 indicates

that samples 401 and 402 were generally identified as green except under LPS,

where they were termed yellow, again raising the possiblity of dangerous misinterpretations. Sample 404 was identified as yellow under all sources closely

matching the performance of ANSI Safety Yellow (130/135). The greater (combined)

absolute frequencies for the latter make those results slightly more convincing,

however. In addition. Safety Yellow is an ordinary color, which can generally

be expected to be cheaper, and less subject to fading than a fluorescent color.

In the 400 series, samples 405-413 were generally termed as orange or red

under all sources with few confusions with other colors such as brown or yellow. Samples 414 and 415, however, had relatively few confusions with

orange or orange red, even under LPS, and thus appeared to be the samples most

uniquely identifed as red of the four series of samples tested, with 414 the

best of all. It should be noted that to excite fluorescence in a pigment, the

incident light must contain wavelengths shorter than the re-emitted (fluorescent)

light. Thus, since LPS consists almost entirely of a narrow band near the

yellow-orange wavelength of 589 nm, it would be expected that only fluorescent

orange and red could be excited under LPS. The results for the 400 series

confirm that expectation.

Because of the Importance of the color red in signalling danger or stop, greater

attention was paid to samples which were named as red in the present study.

Figures 6 to 10 present the redness percentages for all color samples under

each of the five light sources. These figures indicate the fraction of times

the primary color of a sample was identified as red under a given light source. Samples not appearing at all in any of these figures were never identified as red under the specified light source. Figures 11 to 15 present similar data

54
eei 00 U) c\]

«)

&•

f) M

E

9

CE 0*0 eooo CLOtuuo e<p

55

Figure

6.

Percentage

of

trials

in

which

designated

color

samples

were

identified

as

red

under

LPS
100

—

nrn

c

t

• —

1 r-

•

1 -

'

C

r

"

.

'

' "• —

c

c

rC

r--

' " - -~ czz

I —

c

c

CZZZI dZ

c

T

1 1 1

-ST7

-VT*7

-nv

-ZTV

-eov

~20V

-LOV

-90V

-sov

-60 £

-8oe

-^oe

-9ZZ

-szz •nz

‘ZZZ

’ZZZ

T.ZZ

ozz

-6TZ

•8TZ

ITZ

•9IZ

•ZIZ

•TIZ

•lOZ

"iST

-OST

-001

tou

t) U3

I)o.E

10

® G>

00 U)

O ® O ^

CU

q: 0*0 cooo Q.oi.uo c-p

56

Figure

7.

Percentage

of

trials

in

which

designated

color

samples

were

identified

as

red

under

HPS
100

s.

-

1— .

.

. L . :

' ' "

L-. r

- r

{,r

- -

!

”ZI<7

-II

V

-OTV

-60V

-80V

-£0V

-90V

-SOV

-6oe

-80 e -^oe

r~

r. - -

r - - r

!

1

r~

r

I

-zzz

-\zz

-033

-6T3

-813

-ST3

-VT3

-ei3

-313

-II3

tfi u

V

E

EL

E

0

in

-061

-S5T

-ogi

00

o o

cu o

Of 0 ‘T3 0000 Q 0 Lc U 0 0 ^

57

Figure

8.

Percentage

of

trials

in

which

designated

color

samples

were

identified

as

red

under
lee

-Sit?

-t?It?

-ITV

-OTV

-60V

-80V

-40V

-90V

-sov

-6oe

-8oe

-4oe

t) ja

E

O

-SZ3

-V3Z ®

-£ZZ "I -zzz g*

-TZZ 5

-02C

-613 5^

-RT7

r

- - - .... -.z CZ.- ' —

I 1"’ - ' ' -

1

1

1

:

I 1 -

1

L . .

-413

-913

r" -ST3

1 - ' - -*7lZ

CT7 t LC

i -CCT SSL. — nr T Ub 1

1 1 i 1 ® ® ® ® 9

00 (D 'T fU

4-1 c

Q)O

CO

(UO

U

:i

4-1

l-l 0)

'C3a

3

T3

0)U

CO

ccJ

(U •H44

•H

4-) c

(U t3

•H

ck; 0*0 eooo o.ot«oo (V3

bO

•H

P3l4

58

Percentage

of

trials

in

which

designated

color

samples

were
100

czi

•siv

•m

•£Xt7

•TIV

0I<7

60 V

•BOV

L0*7

90V

-SOV

-6oe

-BOB

-£oe

1 - —

f ' - - —

r — ——

r

' '

-9ZZ

-9ZZ

-£ZZ -zzz

-TZZ

-ozz

~6TZ

-8TZ

-LIZ

-m

VI

3

-eiz

-ZTZ

-liz

ft) JQ

E

2Z

a.E

0

iS)

-S5I

-OSI

00

CB> m

(X, ons COeOtf) D_ « % D

59

Figure

10.

Percentage

of

trials

in

which

designated

color

samples

were

identified

as

red

under

tungsten
100 00 U)

^OJ

«)

%•

f)E

P

o i. ID e e>o eo«)«o Q.O&.OI)

60

Figure

11.

Percentage

of

trials

in

which

designated

color

samples

were

identified

as

orange

under

LPS
lee

-m

-Zl*7

-IT^

-OIV

-60V

-80V

-LOV

-90V

-SOV

-m

~LOZ

-90 e -SOG

o

00

o

u> —

r

-6TZ

-m

-913

-4\l

-ZIZ

-OIZ

-603

-803

U

o

o

o.E

10 U)

-SSI

-osi

-GVI

-OVI

fU

o k «f e D>o eoo)«) CLOkuo c<p

61

Figure

12.

Percentage

of

trials

in

which

designated

color

samples

were

identified

as

orange

under

HPS
001

-CIt7

-3TV

-IIV

-01^

-60V

-80V

-iOV

-90V

-SOV

-8oe

-zoe

-9oe -soe -voe

-813

-9X3

-ST3

-0X3

-603

-803

-ssx

U

f)

O.

E

0

V)

O

00

o

(D cu

o i. 0 e t»o C000 0.01.00 e«P

62

Figure

13.

Percentage

of

trials

in

which

designated

color

samples

were

identified

as

orange

under
lee

h6oe

80 e hioe

-9oe

-soe

-VI2

-OTZ

-603

-303

hS9I

SSI

|-sn

•017I

«)

u

I)

4a

p.

E

ID

(X)

o

00 U)

9

(U

o i« 0 e 0)0 eooo Q.oi«oo

63

Figure

14,

Percentage

of

trials

in

which

designated

color

samples

were

identified

as

orange

under

fluorescent
100

c:

-eiv

-3TV

-II<7

-0117

-60V

-80V

-^ov

-90V

-sov

-vov

-90 e -S0£

-voc

-3oe

-m

-913

-SI3

-eiz

-013

-603

-803

<0

t) Ji

E

9

CL

E

fd CD

-S5I

-CSX

-5. VI

-OVI

o

00

o

CD

<S> OJ

O k ID C D)t) et)tf)iO CLDS^Ut) C ^

64

Figure

15.

Percentage

of

trials

in

which

designated

color

samples

were

Identified

as

orange

under

tungsten
for orange. Because fewer color samples were studied for other safety colors

such as blue and green, these data were left in tabular form, and can be

examined in tables 5 to 8.

4.2 COLOR SHIFT DATA

It is also of interest to determine how the color names for a given sample

shifted as a function of the light source. Figures 16 to 19 compare the color

name given for each sample under each light source with the name given under

tungsten light.

Tungsten (incandescent) lamps represent the source with the highest colorrendering index used in the present experiment. (It should be noted that

for "warm” light sources with a correlated color temperature below 5000 K, the

reference source in the definition of the color-rendering index (CIE, 1974),

is a blackbody or Planckian radiator. The spectrum of an incandescent lamp is

close to that of a blackbody radiator, so that these lamps have color-rendering

indices close to 100.) As a result, the appearance of a color under the tungsten

source is the best indication (in the present experiment) of the "true" or "correct" color of a sample. Thus, deviations from a color's appearance under

tungsten would be largely classifiable as a distortion.

Figure 16 presents the shift data from tungsten to LPS; figure 17 presents the

shift data from tungsten to HPS; figure 18 presents the shift data from tungsten

to MH; and figure 19 presents the shift data from tungsten to fluorescent.

These figures enable one to determine the kinds of color shifts and confusions

that occur for a particular sample color relative to tungsten as different

light sources are used.

To construct these figures, only the dominant color name was used. If

50 percent or more of the responses given were for one color name, this was

considered as the dominant name and Included in the color shift plots. Fewer

than 50 percent responses for one name meant that that sample was excluded

from the color shift figures, as having an ambiguous color, not plottable on

the diagram. Samples that were excluded on this basis are listed on the figures. Note that these figures are analogous to correlation scatter plots.

Perfect agreement between a source and the reference (tungsten) source in the

color names used would be Indicated in these diagrams if all the sample numbers

in the body of the table were located along the main diagonal (upper left to

lower right). Otherwise, the more scatter away from this diagonal, the more

disagreement in color name between the source and the tungsten light.

Figure 16 indicates that extensive shifts in color names occurred from tungsten

to LPS. The majority of the color names shifted toward yellow under LPS.

Furthermore, in no case were purple, green, white or gray, seen as such for

any sample series under LPS. This figure demonstrates the extensive color

distortions that occurred for LPS light relative to tungsten. Aside from

fluorescent oranges and reds, which can be seen as such under LPS, all other

colors are seen as varying only in the light-dark dimension. Most observers

labeled light colors as yellow and dark colors as brown, although sometimes

they used gray and black instead. As a rule, white, yellow, and fluorescent

65
Shift Charts

Tungsten to LPS

TUNGSTEN PURPLE BLUE GREEN

LPS

YELLOW ORANGE RED BROWN BLACK GRAY WHITE

Purple

Blue

Green

Yellow

300

301

1

1 Excluded

1 Brown 1 100, 105

1 150, 155

1 165

1 201, 202

1 214, 216

1 217

1 219, 302 Black 1 110

201, 202

205, 206

303

400, 401 402

130, 135 207, 208

304, 403

404

115 203, 204

120, 125

Orange | 140, 145 305, 307 406, 407

1 209, 210 405

1

1 306

1 Red 1 211, 212 411, 412 408, 409 220, 221 223, 224

1 213, 215 413 410, 414 222 225, 226

1 218 415

309

160

170

Gray |

1 180, 185

1 White 1 190, 195

1 310

Figure 16. Color shift data — tungsten to LPS

A comparison of color names given for

each sample under both tungsten and

LPS light

66
Shift Charts

Tungsten to BPS

1

1

1 HPS

TUNGSTEN

I

1

1

PURPLE BLUE GREEN YELLOW ORANGE RED BROWN BLACK GRAY WHITE j

Purple

1

1 100, 105

1 201, 202

Blue 1 110, 115

1 203, 304

1 300

Green 1 125 205,206 400

1 302, 303

1 401, 402

Yellow 1 130, 135

1 207, 208

1 304, 403

1 404

Orange 1 140, 145 305, 306 407

1 209 307, 405

Red

1

1 150, 155 211, 212

1 213, 214 219, 220

1 215, 216 221, 222

1 217, 218 223, 224

1 308, 411 225, 226

1 412, 413 309, 408

1 409, 414

1

1 415

Brown

1

1

1 160, 165

Black

1

1

1 170, 175

1

1 Excluded

1 180, 185 Gray 1 155

1 210

1 301 White 1 306 190, 195 1

1

1

1

406 310 1

Figure 17, Color shift data — tungstea to HPS

A comparison of color names given for

each sample under both tungsten and

HPS light

67
Shift Charts

Tungsten to Metal Halide

1

1

1 Metal Halide

TUNGSTEN

1

1

1

PURPLE BLUE GREEN YELLOW ORANGE RED BROWN BLACK GRAY WHITE

Purple

1

1 100, 105

1 201, 202

Blue 1 110, 115 •

1 203, 304

1 300

Green 1 120, 125

1 205, 206

1 301, 302

1 303, 400

1 401, 402

Yellow 1 130, 135

1 207, 208

1 304, 403

1 404

Orange 1 145 140, 209 406, 407

1 210, 305

1 306, 307

1 405

Red 1 225, 226 218 211, 415

1 213, 214

1 216, 217

1 219, 220

1 221, 222

1 223, 224

1 309, 408

1 409, 410

1 411, 412

1 413, 414

Brown 1 160, 165

Black 1

1 170, 175

1

1 Excluded

1 180, 185 Gray 1 150

1 155

1 212

1 215 White 1 308 190, 195

1

1

1

310

Figure 18. Color shift data — tungsten to MH

A comparison' of color names given for

each saniple under both tungsten and

metal halide light

68
Shift Charts

/ Tungsten to Fluorescent

1

1

1 Fluorescent

TUNGSTEN

1

1

1

PURPLE BLUE GREEN YELLOW ORANGE RED BROWN BLACK GRAY WHITE

Piirple

1

1 too, 105

1 201

Blue 1 110, 115

1 203, 304

1 300

Green 1 120, 125

1 205, 206

1 301, 302

1 303,

1 401, 402

Yellow 130, 135

1 207, 208

1 304, 403

1 404

Orange 1 140, 145

1 209, 210

1 306, 307

1 405, 406

1 407

Red 1 211, 212 150, 155

1 226 213, 214

1 215, 216

217, 218

1 219, 220

1 221, 222

1 223, 224

1 308, 309

1 408, 409

1 410, 411

1 412, 413

1

1 414, 415

Brown

1

1

1 160, 165

Black

1

1

1 170, 175

1

1 Excluded

1 180, 185 Gray 1 225

1 310

1 400 White 1 ±

190, 195

Figure 19. Color shift data — tungsten to fluorescent

A comparison of color names given for

each sample under both tungsten and

fluroescent light

69
yellow are completely indistinguishable under LPS, even in lightness. The

blue appearance of samples 300 and 301 is difficult to explain, but they evidently appeared primarily black with a blue tint. In addition, figure 4 shows

that a very small amount of energy at 400 nm was present in the LPS spectrum.

The blueness may have arisen from this band.

By comparison, the shifts in color name from tungsten to HPS presented in

figure 17 were far less extensive. There was a shift from red toward orange,

as well as a shift from orange and one from green toward yellow, but generally

the shifts in color name were far less extensive than those occurring under

LPS. It is important to remember that these and all other shifts in these

figures are general trends. The appearance of a "red" (or other color) under

any light source depends on the particular pigment or dye used to produce that

color. By choosing the right specific red or orange pigment, the probability

of correct identification under HPS and other sources can be greatly increased.

Figure 18 demonstrates an even greater reduction in color shifts for metal

halide. Unlike either LPS or HPS, a few shifts from red to purple occurred,

as well as a shift of one sample from orange to yellow. Generally, however,

the color names given to samples viewed under metal halide illumination were

the same ones given under tungsten.

Figure 19 compares color names given under fluorescent light with those given

under tungsten. The only shift which occurred under this light was for certain

200 series samples which shifted from red to purple. Otherwise the color names were the same.

Originally, because of the special safety significance of the red-to-orange

range of colors, it was intended to regard red/orange and orange/red as separate

naming categories, distinct from red and orange. A consequence of this provisional arrangement, however, was that the entire range of samples from 404 to

413 was excluded from the color-shift figures, under the 50 percent rule. As

a result, the final decision was to treat the orange/red categories like all

other names with secondary components; namely, to merge them with the primary

name category. Thus, tables 5 to 8 present the frequency responses for red/

orange and orange/red in parentheses, but the former namings are included in

the total count for red, and the latter in the total count for orange, in

tables 5 to 8 and figures 6 to 19.

In these figures, it should be noted that for the sample series 403-415, for

all light sources, there is a marked tendency to call these samples both orange

and red. Although each sample is responded to with one or the other of these

color names more than 50 percent of the time, in very few cases is that name

applied anywhere near 100 percent. Thus, for this series, nominal orange and

red are often confused with each other. A similar distribution of color names

occurs for samples 307 and 308, and to a somewhat lesser extent for 215/ 216,

and 150/155. The marked confusions in color name between many of the red and

orange samples, regardless of light source, raises issues that will be

addressed in the Discussion section. Here, it will suffice to point out that

the fault for any such confusions can lie with either the light sources, or with the samples themselves.

70
5 DISCUSSION

5.1 RECOMMENDATIONS BASED ON SAFETY COLOR RESEARCH

The data presented in the Results section suggest that a set of colors can be

selected from among the four sample series which are more unequivocally recognizable under all illuminants than the current ANSI Z53 standard safety colors.

Further research is desirable before this selection of colors can be regarded

as definitive; however, the research to date supports the idea that a set of

highly identifiable colors can be specified. This set could include colors

such as sample 301 for green, sample 300 for blue, sample 130/135 for yellow,

sample 305 for orange, and sample 414 for red. Of all the samples studied,

these were the most frequently correctly recognized under all 5 sources. It

should be pointed out, however, that the recommended green, as well as any

other green color sample, was not recognized as such under LPS. The suggested

green has the advantage of confusions with innocuous gray rather than yellow

(signaling caution) under LPS. Use of a fluorescent green is not effective

for LPS because the rule for everyday fluorescence is that the stimulating

wavelength must be shorter than the wavelength of the re-emitted (fluorescent)

light. Since almost all the energy in the LPS spectrum is in a narrow band

near 589 nm, in the yellow-orange part of the visible spectrum, such light can excite only longer-wavelength orange or red fluorescence. Consequently,

obtaining green fluorescence under LPS appears out of the question, except

possibly through unusual physical mechanisms.

Recommendations for purple, brown, gray, white, and black would, according to

the experimental results, follow the existing ANSI Z53 standard (samples 100/

105; 160/165; 170/175; 180/185; and 190/195). Although these particular colors

performed very poorly under LPS light, no other sample performed any better

under this light source. (Very few other samples were studied for these colors.)

Fortunately, these five colors serve primarily as background or outline colors

in the ANSI system, rather than coding this kind of safety message. [Note that,

because red is confused with black under LPS, red on black signs (or vice

versa) would have very low legibility under this source; and yellow on white

(or white on yellow) signs—never very visible at best—are unlikely to be

legible at all under LPS. It should be recalled that under LPS, no distinction can be maintained between white and yellow, even fluorescent yellow.

Because the whole environment appears yellow, it may be inadvisable to use

yellow in its traditional role of signaling caution, under LPS. Orange

(fluorescent) is available for this role, if another degree of warning short

of the danger message of red is desired for this light source.]

It is of interest that three of the colors in the suggested set are from the

300 series—that is, they are retroref lective, and sample 305 is also fluorescent.

There is no obvious reason why the retroref lective property of these samples

should have been of value in improving color recognition, since the illumination

was essentially diffuse and the retroref lective component of the light reaching

the subject's eye was presumably very small. Thus, it can be tentatively

assumed that it was the specific colorants (pigments or dyes) used in these

300-series samples that made them so recognizable. It is not reasonable that

the special requirements of retroref lective materials would necessitate the

71
use of colorant formulations differing from those responsible for the colors

of the other three series of samples. It must be stressed that even colors

that appear identical under daylight or incandescent light may appear different

under other light sources (the phenomenon termed metamerism), as long as the

samples have significantly different spectral reflectance curves; i.e., if the

colors of the samples arise from different pigment or dye mixtures, or if one

color is due to a pigment and the other to a chemically distinct dye. Evidently,

the particular colorants used in samples 300, 301, and 305 are better, in

terms of stability of color appearance under changes of light source, than are any of the approximately corresponding colorants in the ordinary and purefluorescent samples. Future experimentation is advisable in which nonretroref lective samples prepared from these same colorants are tested. Such

samples could be equally as identifiable as the retroref lective ones and might

be cheaper to prepare.

In general, another experiment would be desirable to determine that the five

key color samples listed above are accurately recognized under different

illuminants (including ones not included in this study) by a larger group of

subjects—more representative of the workplace population—and to confirm that

these colors are not confused with each other. It will also be appropriate

in the future to test other colors, since samples which are superior in stability of appearance to those suggested by this study may already exist, or may

be developed.

Another factor to consider is that the viewing conditions used in the present

experiment were deliberately chosen to represent a worst-case situation; i.e.,

the colors were presented in an environment with no other chromatic information.

In the future, it would be informative to repeat the study with more commonplace viewing conditions—either in the field or in a laboratory situation.

In both cases, a number of familiar colored objects could be in view throughout

the experiment. It would be expected that under such conditions, correct

identifications under all light sources, with the likely exception of LPS,

would improve.

The confusion between orange and red obtained with samples from both the 300

and 400 series, suggests that it is difficult to formulate an orange that is never called red, or a red that is never called orange. Furthermore, this

pattern of confusions occurs across all light sources. In addition, of course,

under each separate light source, specific red samples will shift toward orange

and vice versa, thus complicating the picture even further. It would not be

proper to conclude, however, that these red-orange confusions are due in every

case to the light sources used in the experiment. Two much more likely causes

can be pointed out. First, the basic, "unique" hues of color perception are

red, yellow, green, and blue. Orange is a mixture of red and yellow, and

accordingly can be expected to resemble red (or yellow) considerably more than

yellow resembles green, green resembles blue, or blue resembles red. Thus,

red and orange intrinsically resemble each other more than most of the other

pairs of colors studied. Secondly, a substantial number of the red samples

tested were known in advance to be somewhat orangish. ANSI Red was deliberately

chosen to be on the orange side, because that choice makes it easier for one

72
class of red-green color-defective observers (the protans) to distinguish the

red from black. In addition, most fluorescent red pigments, for physical

reasons tend to be somewhat orangish. (It should be noted that the Coast

Guard (1980) in its specification for fluorescent colors does not even attempt

to distinguish fluorescent red and orange, but instead defines a single

fluorescent red-orange color.) Therefore, the many red-orange confusions found

in the present experiment may well be attributable to the particular samples

used, and to the perceptual similarity of any red to any orange.

Confusions between safety colors other than red and orange were not nearly so marked, and tended to be more specific to a particular source. Thus, under

all sources, colors called yellow under tungsten light were rarely seen as orange and almost never as red. Yet, colors called orange under tungsten were

fairly often called yellow under both LPS and HPS, and occasionally under

metal halide. These data suggest that the current use of red and yellow to

Indicate two different degrees of hazard is practical under a variety of light

sources, with a judicious choice of the red and the yellow. Proposals to use

red, yellow, and orange to indicate three levels of hazard appear likely to

prove unworkable because such fine color discriminations cannot always be

maintained. Indeed, table 5 reveals that even under more than 30 fc (vertical)

of tungsten light—essentially perfect in color-rendering index—the current

ANSI Red was called orange 5 out of 22 times, and the ANSI Orange was called

yellow 1 out of 19 times. No such confusions were seen for ANSI Yellow under

tungsten light.

5.2 SUPPORTING RESEARCH

Jerome (1977) pointed out the possibility of confusions between the various

ANSI Safety Colors when viewed under some high-intensity discharge (HID) lights.

He commented that "The ANSI safety colors were designed, and very carefully

specified, to be uniquely identifiable at all times. This identification is

intended to be possible without any other clues, i.e., it must depend only on

the identif lability of the single colors viewed alone" (Jerome, 1977, p.l80).

Jerome asked 20 observers to indicate the primary color (no secondary color

allowed) of a set of safety colors (the 100 series from the present study)

under each of six lamps (daylight fluorescent, incandescent, metal halide,

deluxe mercury, clear mercury, and high pressure sodium). Low pressure sodium

was not used because the author concluded that all ordinary colors seen under

this source were confused, and that any color differences were due to lightness

differences. Sample illuminance was quite low, 0,5 fc, much lower than in the

present experiment. Jerome chose this level because it is the minimum specified level for emergency lighting. Jerome calculated the percentage of correct

identifications and confusions for each safety color. He found that major

confusions arose for both types of mercury lamps and high pressure sodium. As

in the present study for the 100 series, under HPS ANSI Red and Orange were

confused with each other and ANSI Green was often seen as blue. Under metal

halide, safety Red was often confused with orange. (In the present study,

ANSI Red (150/155) could not be given a dominant color name under metal halide,

because of extensive confusions between orange and red, plus occasional

responses of yellow and brown.) Jerome also found a few red-orange confusions

73
for incandescent light—confusions that also arose in the present study.

Thus, in general trends, Jerome's data certainly support those from the

present study.

Where detailed differences arose, such as greater confusions in his study

between blue and black or white and yellow, they may well be due to the very

low Illumination level used by Jerome, as well as his use of a different set

of light sources.

"The net conclusion is that there are some light sources being used extensively

under which the [current ANSI standard] safety colors cannot be Identified

positively with any degree of certainty. Under these circumstances, if the

safety colors are to perform their assigned function, supplementary lighting

must be provided for the colors under which their identification can be determined without ambiguity” (Jerome, 1977, p. 182). A comparison of the calculated

CIE color rendering index for the samples under the various light sources,

with the percentage of correct identifications, indicated very poor correlation

between the two measures. Jerome (1977, p. 182) commented that "Apparently,

the answer is not how faithfully the colors are rendered, the attribute indicated by the Color Rendering Index, but how well the colors can be perceived

as different from the other colors. That is, if the red can be identified as red and not some other color, even though it may differ greatly from its

daylight appearance, it is performing its function as a safety color

satisfactorily.

To deal with the problem of safety colors under HID or other illumlnants,

Thornton (1977) proposed that the colors themselves, rather than the lights,

should be redesigned. He asked: "How can we redesign the safety-colors for

maximum stability of perceived color with change of illuminant; i.e., so that

all present and future commercial lamps have the best chance of rendering the

safety-colors so they are easily and correctly identified?" (Thornton, 1977,

p. 93). He suggested that the best way to achieve the redesign was to alter

the spectral reflectance distributions of the safety colors, by using fluorescent colors for red, yellow, orange, and purple samples. This approach was taken for the series 400 colors in the present experiment, as well as for some

of the 300 series. (No fluorescent purple sample was acquired, however.) Of

course, in addition to the safety colors, the illuminant itself could be modified to allow maximum color discrimination capability (Thornton, 1977).

Boyce and Simmons (1977) investigated the effects of light source and

illuminance level on a much finer hue-discrimination task. Using the

Farnsworth-Munsell 100-Hue test, they measured hue discrimination performance

under a variety of light sources. These sources were, however, primarily

fluorescent sources, so that no data was obtained for HID sources such as metal halide, LPS, or HPS. The 100-Hue test consists of 85 colored discs

arranged in approximately equal perceptual steps, around the complete hue

circle, with constant saturation and lightness. Lamp type, but not, in

general, illuminance level, was found to affect performance significantly.

Age, but not experience with the 100-Hue test, was also found to affect

performance significantly, with those over 55 making significantly more errors. The authors concluded that while age may determine the general level of errors.

74
there is also an indication that for older subjects, performance is better at

higher illuminance levels. The error scores indicated that lamps with "poor

color properties" produce more errors than those lamps with "good color properties". The choice of light sources as well as the age of the observer determines the discriminability of colors far more than did the illuminance level

or observer's experience. This study, although it did not use the high or low

pressure sodium lights demonstrated to cause problems in color rendition in

other experiments, did demonstrate that variations in the illuminant alone

impair performance on the 100-Hue test.

Another study by Ronchi and Stefanacci (1978) also assessed performance on

the 100-Hue test under HPS light. It demonstrated that errors increased under

HPS relative to illuminant C at 70 lux and that these errors were similar to

those exhibited by color deficient observers. A tritan-like effect occurred

under HPS for about one-half the subjects and a mixed protan/deutan effect for

about one-third. See figure 1 parts a, b, and c for examples of each type of

confusion and section 2.3 for definitions.

The studies which have assessed color discriminability under various light

sources have demonstrated a clear decrement in performance, especially for HPS

and LPS. Results from the present study suggest that use of fluorescent and

retroreflective-f Increscent colors may increase correct color identification

particularly for the red and orange colors under all sources, and for blue and

green under all sources except LPS. These results bear out the recommendations

made by Thornton (1977) that modification in the safety colors themselves may

be one of the best ways to ensure their discriminability.

75
6 RECOMMENDATIONS

.

6.1 APPLICATIONS TO THE WORKPLACE

The results of the present experiment combined with those by Jerome (1977) and

the suggestions by Thornton (1977) indicate clearly that use of the current

ANSI Safety Colors under some HID light sources is not advisable if accurate

color recognition is desired. Two solutions suggest themselves: modify the

lighting, or modify the spectral distribution of the safety colors themselves,

by using fluorescent pigments or dyes (such as those used in the fluorescent

400 series, or in the retroref lective-f luorescent 300 series samples).

Using the latter approach in the present study, a set of highly identifiable colors was Isolated for further study. These colors appear to be

discriminable under a wide variety of HID and other lamps, including

partial discriminability even under LPS.

If conventional ANSI Safety Colors are to be used, the use of LPS as the light source is not recommended, as most of the current safety colors are not identifiable under this source. If the decision is made to continue using the con- ventional ANSI Safety Colors, then the LPS or other poor color-rendering

lighting system should be modified, at least for critical signs. There are a number of possibilities in this approach. The first, which is perhaps the

easiest way to ensure good color recognition, is to switch the lamps to ones with good color rendition. With this approach, cost becomes a factor, as good

color rendering sources are often more expensive to operate. The second alternative is to mix luminaires using both good and poor color-rendering sources

over an entire area. While this solution will be less expensive than the

first, the best mixtures of lllumlnants for accurate color recognition combined

with good energy efficiency (luminous efficacy) is not presently known. A

third possibility is to add a small, supplementary, good color-rendering source directly over the sign Itself. This localized lighting will illuminate the

safety sign itself, and facilitate accurate color recognition. It does, however, require either a battery or an electric power outlet near the sign. In

many cases, it may be advantageous for color recognition to shade the sign at

least partially from the color-distorting general lighting. The final possibility is the use of powered, self-luminous signs. Such signs are widely used

for conventional exit signs; their use could be extended to signs warning of

highly hazardous conditions. The use of localized lighting or self-luminous

signs appears to be a reasonable solution in areas where general LPS or any

very poor color-rendering lighting source is already installed. This alternative also appears to be the only means of ensuring that green is recognized as green under LPS light, since all green color samples were poorly recognized

under LPS in the present study.

6.2 PROBLEMS OF COMPLIANCE

If the current ANSI Safety Color Standard, Z53.1 (1979) were to be revised to

specify the set of color samples currently identified as being most recognizable

under all sources in the present experiment, how would a safety officer in a workplace determine whether colors in that workplace complied with the new

standard? One might think of using a small, inexpensive colorimeter, to do

76
this job. Unfortunately, at this point the experimental set contains both

retroref lective and fluorescent colors, both of which are very difficult to

measure under non-laboratory conditions. The reader is referred to Billmeyer

(1979) for a discussion of the procedures to follow when measuring fluorescent

colors and calculating spectral total radiance factors under daylight illumination. The reader is referred to Eckerle (1980) for a discussion of the accuracy

of measurements of retroref lective colors, as well as the present inadequacy

of field-measurement methods.

An even simpler idea would be to produce a set of color tolerance charts for

the new colors, analogous to the U.S. Department of Transportation’s Hazardous

Materials Label and Placard Color Tolerance Charts (1973), which performs this

role Cor the current ANSI Safety Colors. Theoretically, no set of color tolerance charts is a valid compliance device if the on-site illumination differs

significantly in its spectral power distribution from the light source for

which the charts were standardized. However, if it can be agreed that the set

of colors suggested by the present experiment appear correct under any of the

current commercial sources (with appropriate exceptions for LPS), then a set

of color tolerance charts might be feasible. The chart colors would all look

somewhat different under each source, but with the chart colors and the workplace colors all illuminated by the same source, it would be reasonable to

allow the color under test to be in compliance if it lay visually within the

range of the limit colors on the chart. Developing the limit colors for such

a chart is a major project. The limit colors would have to be composed of

different proportions of the same pigments or dyes as the standard colors, to

avoid differential appearance-shifting with a change of light source (minimizing metamerism). Moreover, the determination of how far off from the

standard color one should be allowed to deviate in hue, saturation, and lightness, would have to be made on the basis of careful color-naming experiments,

such as the one reported here.

Since the concern in safety-color standardization is appearance (does the

supposedly red color look red), one is forced to conclude that any valid com- pliance method possible at this time, if it is to apply uniformly to any source,

must be based on visual judgments and cannot be Instrumental, even if sufficiently accurate and inexpensive measuring instruments were available. This

conclusion is a result of the phenomenon of chromatic adaptation, a significant

factor for determining color appearance for people working under any light

source. Figure 20 illustrates this point clearly. The five vertices of the

pentagon locate the chromaticities of the current basic ANSI Safety Colors

illuminated with HPS light. Note that all the chromaticities lie in what is

normally thought of as the orange region of the chromaticity diagram, even

that of ANSI Blue. [That point lies between the daylight (white) point and

the orange part of the spectrum locus.] However, table 5 shows that ANSI Blue

(sample 110/115) is always seen as blue under HPS, not as orange or anything

else. To allow chromaticity (and reflectance) measurements by a machine

to determine compliance with a color standard that applies to all sources, it

would be necessary to determine through color-naming experimentation, the

chromaticity limits that lead to each desired color perception under adaptation

to each separate light source . This would require the gathering of a great

77
VALUES OF X

Figure 20. Chromaticities of standard ANSI colors illuminated with

HPS light

78
deal of perceptual data, after which a set of many chromaticity-limlt tables

(one for each type of light source) would have to be supplied along with the

measuring instrument.

6.3 RECOMMENDATIONS FOR FURTHER RESEARCH

One of the areas for which further research is needed has already been discussed

but will be mentioned here again. This is the need to evaluate the performance

of the set of safety colors identified as "most recognizable" from the present

study, using a wider set of variables. This would include more observers,

different illuminance levels, additional light sources (mercury, as well as any new sources), different adaptation times, and of course, any promising new

color samples that have recently come into the market, such as new fluorescent

colors or ordinary colors especially formulated to appear correct under HID

sources. This experiment would determine if these samples are in fact effective under a wider set of controlled experimental conditions. This research

should then be extended to field conditions, in which the discriminability and

recognizability of signs using these colors in industrial settings would be

assessed.

Another area in which further research is needed is that of chromatic

adaptation. How long does adaptation to a monochromatic source, such as LPS

last, and how great is the distortion in color recognition following exposure

to such a source? If a person moves from an area lighted by one of these sources to an area lighted by another source, how accurately will the colors

be perceived under the new source? Thus, both the time course and extent of

chromatic adaptation need to be determined experimentally for different types

of light sources. In addition, the magnitude of the distortion in color

appearance due to chromatic adaptation should be determined for the color

samples identified in this study.

An important long-range research project is the development of a formula for

predicting the color appearance of any color sample under any light source,

with no further necessity for perceptual experimentation whenever a new light

source is marketed. Such a formula does not yet exist. Developing and validating this formula would require enormous amounts of perceptual experimentation,

as well as of computer optimization of the constants for the formula, based on

the perceptual data. Success, however, would mean predicting from the spectral

reflectance curve of an arbitrary sample, and the spectral power distribution

of an arbitrary source, the appearance that the sample would have if illuminated

by that source and viewed by a person adapted to that source. The prediction

might be in the form of the chromatidty (x,y) and luminous reflectance (Y) of

a sample which has this same appearance when illuminated by and viewed under

adaptation to a fixed reference source, such as the CIE daylight (D65) source.

The possibility of mixing sources which differ in their color-rendering

capabilities has already been addressed, but the need to determine the optimum

ratio of the source Illuminances for a good balance between accurate color

recognition and energy efficiency remains. Can an area be lighted primarily

with LPS or similar poor color-rendering lights, to reduce lighting costs,

with the addition of a few good color-rendering sources, and still allow good

79
color recognition? What is the optimum balance, in terms of total life-cycle

cost of the lighting installation and color recognition? Again, a laboratory

investigation is needed to determine, for each energy-efficient light source,

the minimum proportion of the good color rendering light source needed to

allow acceptable color recognition. If the proportion is too high, then the

installation becomes too expensive, and defeats the use of the high-efficiency

light sources. If the fraction is sufficiently low, then mixing light sources

becomes a good way to solve the problem of color distortion under that particular energy-efficient source.

Along the same lines, some modification of the high-efficiency light sources themselves to Improve color rendition is possible. This job has already been

started with the advent of such new sources as color-improved HPS. Commonly,

Improving the color rendering of a given type of light source results in some

loss of luminous efficacy. The optimum tradeoff point, either for the modification of a single source, or for mixing two different sources (in a room or similar area), will depend on the relative valuations (weighting) assigned by

the user to saving energy and/or money, and to being able to recognize and

discriminate colors with accuracy. Accordingly, a full solution to the problem

involves determining not a single optimum compromise, but a set of such values,

varying with the user-assigned weighting.

6.4 CAPSULE SUMMARY

The results of the preliminary laboratory research suggest strongly that the

present safety colors do not adequately convey accurate chromatic information

under many of the HID sources. A set of safety colors which appear more

universally recognizable have been identified, but further research is sug

gested to validate this finding. Further research is also needed to determine the feasibility of using these colors on signs in industrial settings.

80
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81
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of Michigan, Ann Arbor, Michigan, March 1978.

15. Christ, R. E., Review and Analysis of Color Coding Research for Visual

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Safety and Health Administration, 1981.

18. Code of Federal Regulations, Title 49, Transportation^ Parts 100-199,

Hazardous Materials Transport Labels, January 1974.

19. Collins, B. L., Use of Hazard Pictorials/Symbols in the Minerals Industry

NBSIR, in preparation, 1983.

20. Collins, B. L. and Pierman, B. C., Establishing Ways to Decide Whether

People Understand Symbols, Industrial Design , 26, pp. 48-50, 1979.

21. Collins, B. L., Lerner, N. D., and Pierman, B. C., Symbols for Industrial

Safety, NBSIR 82-2485, April 1982.

22. CIE (Commission Internationale de I'Eclairage) , Method of Measuring and

Specifying Color Rendering Properties of Light Sources, CIE Publication

No. 13.2 (TC32), Paris, 1974.

23. Cornsweet, T. N. , Visual Perception , New York: Academic Press, 1970.

24 Craik, K. J. W. , The Effect of Adaptation Upon Visual Acuity, British

Journal of Psychology , 29, pp. 252-266, 1939.

25. Department of Transportation, Federal Highway Administration, Manual on

Uniform Traffic Control Devices for Streets and Highways , U.S. Department

of Transportation, Federal Highway Administration, Code of Federal Regula

tions. Title 23, 1979.

26. Douglas, C. A. and Booker, R. L., Visual Range: Concepts, Instrumental

Determination, and Aviation Applications, National Bureau of Standards,

NBS Monograph 159, June 1977.

27. Easterby, R. S. and Hakiel, S. R. , Safety Labelling and Consumer Products

Field Studies of Sign Recognition, AP Report 76, Applied Psychology

Department, University of Aston in Birmingham, Gosta Green, Birmingham,

England, December 1977.

28. Eckerle, K. L., Photometry and Colorimetry of Retroref lection: Stateof-Measurement-Accuracy Report, National Bureau of Standards, Technical

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82
29. Fry, G. A., Quantitative Formulation of Color Mixture and Chroma

Discrimination Data for Dichromats, Journal of the Optical Society of

America , 34, pp. 159-167, 1944.

30. Hecht, S. and Mintz, E. U., The Visibility of Single Lines at Various

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31. Hecht, S., Shlaer, S., Smith, E. L., Haig, C., and Peskin, J. C., The

Visual Functions of the Complete Color Blind, Journal of General

Physiology , 31, pp. 459-472, 1948.

32. Higgins, G. C. and Stultz, K. , Visual Acuity as Measured with Various

Orientations of a Parallel-line Test Object, Journal of the Optical

Society of America , 38, pp. 756-758, 1948.

33. Howett, G. L., Size of Letters Required for Visibility as a Function of

Viewing Distance and Observer Visual Acuity, NBS Technical Note, in

preparation.

34. Howett, G. L., Kelly, K. L., and Pierce, E. T., Emergency Vehicle

Warning Lights; State-of-the-Art. National Bureau of Standards, NBS

Special Publication 480-16, September 1978.

35. Hurvich, L. M. , Color Vision, Sunderland, Mass: Sinauer Associates,

1981.

36. lES (Illuminating Engineering Society), lES Lighting Handbook , Reference

Volume, New York, NY, 1981.

37. International Labour Office, Encyclopedia of Occupational Health and

Safety , New York: McGraw-Hill, 2, 1972.

38. ISO (International Organization for Standardization), Safety Colors

and Safety Signs, Geneva: ISO, Draft Standard, DS 3864.3, ISO/TC 80,

1978.

39. Janda, H. F. and Volk, W. N., Effectiveness of Various Highway Signs,

National Research Council — Highway Research Board Proceedings , 14,

pp. 442-447, 1934.

40. Jerome, C. W. , The Rendering of ANSI Safety Colors, Journal of the

Illuminating Engineering Society , 6, pp. 180-183, 1977.

41. Judd, D. B., Color Perceptions of Deuteranopic and Protanopic Observers,

Journal of Research at the National Bureau of Standards, 41, pp. 247-271,

1948.

42. Judd, D. B., The Color Perceptions of Deuteranopic and Protanopic

Observers, Journal of the Optical Society of America, 39, pp. 252-256,

1949.

83
43. Judd, D. B. and Wyszecki, G., Color In Business, Science and Industry , New York: John Wiley and Sons, Second Edition, 1963.

44. Kelly, K. L. and Judd, D. B., Colon Universal Language and Dictionary

of Names, NBS Special Publication 440, December 1976.

45. Krill, A. E., Abnormal Color Vision. In A.M. , Potts (Eds), The

Assessment of Visual Function , St. Louis: The C. V. Mosby Company,

pp. 136-157, 1972.

46. Lakowski, R. , Theory and Practice of Colour Vision Testing: A Review,

Part I, British Journal of Industrial Medicine , 26, pp. 265-288, 1969.

47. Laner, S. and Sell, R. G., An Experiment on the Effect of Specially

Designed Safety Posters, Occupational Psychology , 34, pp. 153-169,

1960.

48. Lerner, N. D. and Collins, B. L., Workplace Safety Symbols, National

Bureau of Standards, NBSIR 80-2023, 1980.

49. Linksz, A. and Waaler, G. H. M. , Naming of Groups with Normal Color

Vision, Nature , 219, pp. 687-688, 1968.

50. Ludvigh, E., Extrafoveal Visual Acuity as Measured with Snellen TestLetters, American Journal of Ophthalmology , 24, pp. 303-310, 1941.

51. Mandelbaum, J. and Sloan, L. L., Peripheral Visual Acuity with Special

Reference to Scotopic Illumination, American Journal of Ophthalmology , 30, pp. 581-588, 1947.

52. Middleton, W. E., Vision Through the Atmosphere , Toronto: University of

Toronto Press, 1963.

53. National Safety Council, Accident Facts : 1979 Edition, National Safety

Council, Chicago, 1979.

54. Ogilvie, J. C. and Taylor, M. M. , Effect of Orientation on the

Visibility of Fine Wires, Journal of the Optical Society of America , 48, pp. 628-629, 1958.

55. Ronchi, L. and Stefanacci, S., Colour Discrimination in the Frame of

Illuminating Engineering, Modem Problems in Ophthalmology , 19,

pp. 88-91, 1978.

56. Rubin, M. and Walls, G. L., Fundamentals of Visual Science , Springfield,

111: Charles C. Thomas, 1969.

57. Saenz, N. E. and Riche, C. V., Jr., Shape and Color as Dimensions of

a Visual Redundant Code, Human Factors, 16, pp. 308-313, 1974.

84
58. Schade, 0. H. , Optical and Photoelectric Analog of the Eye, Journal

of the Optical Society of America , 46, pp. 721-739, 1956.

59. Schiff, W. Perception; An Applied Approach , Boston; Houghton Mifflin,

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60. Shlaer, S. The Relation Between Visual Acuity and Illumination,

Journal of General Physiology , 21, pp. 165-188, 1937.

61. Shlaer, S., Smith, E. L., and Chase, A. M. , Visual Acuity and

Illumination in Different Spectral Regions, Journal of General Physiology , 25, pp. 553-569, 1942.

62. Shontz, W. D., Trumm, G. A., and Williams, L. G., Color Coding for

Information Location, Human Factors , 13, pp. 237-246, 1971.

63. Sloan, L. L., Measurement of Visual Acuity; A Critical Review, A.M.A.

,

Archives of Ophthalmology , 45, pp. 704-725, 1951.

64. Sloan, L. L., The Photopic Acuity-Luminance Function with Special

Reference to Parafoveal Vision, Vision Research , 8, pp. 901-911, 1968.

65. Smith, D. 0., Color Naming and Hue Discrimination in Congenital Tritanopia

and Tritanomaly, Vision Research , 13, pp. 200-218, 1973.

66. Smith, S. L. Letter Size and Legibility, Human Factors , 21, pp. 661-670,

1979.

67. Smith, S. L. and Thomas, D. W. , Color Versus Shape Coding in Information

Displays, Journal of Applied Psychology , 48, pp. 137-146, 1964.

68. Thomas, J. P., Spatial Resolution and Spatial Interaction in E. C.

Carterette and M. P. Friedman (Eds.), Seeing, Vol. V, Handbook of Perception , New York; Academic Press, pp. 233-264, 1975.

69. Thornton, W. A., The Design of Safety Colors, Journal of the Illuminating

Engineering Society , 6, pp. 92-99, 1977.

70. Treasury Board Canada, Graphic Symbols for Public Areas and Occupational

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71. Vos, J. J. and Walraven, P. L., On the Derivation of the Foveal Receptor

Primaries, Vision Research , 11, pp. 799-818, 1970.

72. Walker, R. E., Nlcolay, R. C., and Stearns, C. R. , Comparative Accuracy

of Recognizing American and International Road Signs, Journal of Applied

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85
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Quantitative Data and Formulas, New York: Wiley, 1967.

86
APPENDIX A: ADDITIONAL DETAILS OF THE ILLUMINATION IN COLOR LABORATORY

In the Illumination Color Laboratory, illumination could be provided by one

of the six different systems. These systems Included low pressure sodium

(LPS), high pressure sodium (HPS), metal halide (MH) , fluorescent (FL),

mercury and incandescent tungsten (T). One metal halide, one clear mercury,

and one high pressure sodium light was positioned above each of the two lateral

sides of the chamber. (Note, clear mercury was not included as a light source

in the present experiment.) Each of these lamps was located inside a large,

hemispherical aluminum reflector, which was oriented upward at an angle, so

as to throw light toward the ceiling of the room, above the chamber itself.

This upper ceiling was covered with a specularly reflective material, to

reflect the light downward onto the double diffusing ceiling of the illumination chamber. The resulting folded optical path was necessitated by the

limited space available within the main room. Shutter panels were placed

directly in front of each reflector to control illumination levels. No electronic dimming was used. Two tungsten floodlight lamps were located above the

front area of the chamber ceiling, and four were located in the rear. Five

fluorescent tubes and eight low pressure sodium lamps, all without reflectors, were located on a motorized carriage, that could be moved into and out

of place above the illumination chamber ceiling. To avoid interfering with

the light distribution, this carriage was moved out of the chamber when any of

the other sources was used.

Three of the walls of the chamber consisted of sheets of painted

canvas. Each wall was formed from a large canvas roll painted sequentially in

six different colors. Different sections of the roll could be cranked into

place, thus permitting wall color and reflectance value to be varied. Although

the wall color could be changed to one of six colors, (black, gray, white,

red, green, and blue), only black walls were used in the present experiment.

The fourth and removable wall panel, constructed of plywood with a black,

felt-like fabric surface, contained a 5 in. by 7 in. viewing area for sample

presentations. This viewing shutter was covered with the same black fabric,

as the rest of the wall panel, when the shutter was closed. During the experiment, the shutter could be raised to expose color samples to be viewed by the

observer. Two layers of translucent plastic diffusers formed the chamber

celling and provided even light distribution. (The floor was covered with

gray tile speckled with irregular, light spots.)

87
APPENDIX B: LIST OF DOCUMENTS COMPLETED DURING THE OSHA/NBS RESEARCH

The following documents and workshops were completed during the course of the

OSHA-sponsored project on criteria for signs and color in workplaces.

o Eckerle, K. L., Photometry and Colorimetry of Retrof lection: State-ofMeasurement-Accuracy-Report , NBS Technical Note 1125, July 1980.

o Kaetzel, L. J., Glass, R. G, and Smith, G. R. , A Compter Data Base

System for Indexing Research Papers, NBS Technical Note 1123, October 1980,

also in Behavior Research Methods and Instrumentation, 12(5), pp. 547-548,

1980.

o Calabrese, J. M. , Kaetzel, L. J., Glass, R. G., and Smith, G. R. , A

Computer Data Base Systm for Indexing Research Papers, NBS Technical

Note 1167, October 1967.

o Instrumental Photometric Measurements of Retrof lective Materials and

Retrof lectlve Devices, Federal Test Method Standard 370, March 1, 1977.

o Fearn, J. E., Durability of Signage on Workplaces: A State of the Art

Report with Suggestions for Research, June 19, 1978.

o Billmeyer, F. W. , Colorimetry of Fluorescent Specimens: A State-of-theArt Report, National Bureau of Standards, NBS-GCR 79-185, (NTIS

No. PB-80-165-590) , October 1979.

o Glass, R. A., Color Perception Under Energy Efficient Lights. Presented

at Light, Health, and Design Conference, May 20-22, 1981, Ottawa, Canada.

(Sponsored by Health Facilities Design Division, Health Services and

Promotion Branch, National Health and Welfare.)

o Center for Building Technology, Special Workshop on Color and Vision in

Buildings, December 9, 1980.

88
IX . M4A (REV. 2-ec) U.S. DEPT. OF COMM. 1. PUBLICATION OR 2. Per orming Organ. Report No. 3. Publication Date BIBLIOGRAPHIC DATA

REPORT NO.

April 1983 SHEET (See instructions) NBSIR 83-2694

4. TITLE AND SUBTITLE

SOME CRITERIA FOR COLORS AND SIGNS IN WORKPLACES

5. AUTHOR(S)

Robert A. Glass, Gerald L. Howett, Karen Lister and Belinda L. Collins

6. PERFORMING ORGANIZATION (If joint or other than MBS, see instructions)

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No.

8. Type of Report & Period Covered

Final 1978-1983

9.

SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City, State, ZIP)

Occupational Safety and Health Administration

Department of Labor

200 Constitution Avenue

Washington, D.C. 20210

10.

SUPPLEMENTARY NOTES

[] J Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11.

ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here)

The use of safety-related visual displays such as signs and colors in workplaces is

discussed. The discussion includes a review of relevant national and international

standards for safety colors and signs. It also includes a review of measures of spatial

resolution in human vision, as well as of color sensitivity and color appearance. In

addition, research on the effectiveness of safety signs, symbols, and colors is reviewed

Based on the initial literature review, the appearance of safety colors under energy . efficient light sources was identified as an area for detailed research. As a result,

a laboratory study was conducted in which the color appearance of 45 different color

samples under five light sources including energy efficient ones was determined for

seven subjects. The color samples were contained in four color series t standard colors;

experimental colors; retroreflective and retroreflective-f luorescent colors; and

fluorescent-only colors. The results indicated the existence of a set of colors which

was more identifiable under all light sources than the current standard safety colors.

This set contains a number of fluorescent and retroref lective colors, unlike the

current safety colors. Recommendations are made for further research, including field

research, to determine the effectiveness of the suggested color set on safety signs

under an even broader range of illuminants. The need to assess color appearance under

mixed light sources is also addressed.

12.

KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons)

Chromaticity ; color; color appearance; energy-efficient lights; illvimination;

light source; safety; safety sign; safety symbols; visual acuity; visual sensitivity.

13. AVAILABILITY

nkl Unlimited

I I For Official Distribution. Do Not Release to NTIS rn Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402.

Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

97

15. Price

$11.50

USCOMM-DC 6043-P80
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