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Equal Apparent Conspicuity

Contours With Five-Bar Grating

Stimuli

Gary T. Yonemura

Edward J. Rinalducci*

Robert L. Tibbott

Linda A. Fogelgren*

Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

U S. Department of Commerce

Washington, D.C. 20234

‘Department of Psychology

University jf Virginia

Charlottesville, Virginia 22901

May 1980

Prepared for: Architectural and Engineering Systems Branch

Division of Building and Community Systems

r^ffice of the Assistant Secretary

“QC

100

.056

79-1925

1980

>nservation and Solar Applications

apartment of Energy

ashington. D.C. 20545

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NBSIR 79-1925

I . < EQUAL APPARENT CONSPICUITY

CONTOURS WITH FIVE-BAR GRATING

STIMULI

Gary T. Yonemura

Edward J. Rinalducci*

Robert L. Tibbott

Linda A. Fogelgren*

JUL 1 1 1980

not att.

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Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

U.S. Department of Commerce

Washington, D.C. 20234

*Department of Psychology

University of Virginia

Charlottesville, Virginia 22901

May 1 980

Prepared for; Architectural and Engineering Systems Branch

Division of Building and Community Systems

Office of the Assistant Secretary

Conservation and Solar Applications

Department of Energy

Washington, D.C. 20545

U.S. DEPARTMENT OF COMMERCE, Philip M. Klutznick, Secretary

Luther H. Hodges, Jr., Deputy Secretary

Jordan J. Baruch, Assistant Secretary for Productivity, Technology, and Innovation

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director
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CONTENTS

Page

Abstract iv

Introduction 1

Background 2

Five-Bar Grating Pattern Experiment 3

Subjects 3

Stimuli 3

Lighting System 8

Procedure 8

Results 11

Discussion 11

References 31

Appendix A 32

ABSTRACT

The report discusses the results of laboratory studies on equal

conspicuity (contrast) contours using as the test stimuli five-bar

grating patterns, with the results of other experiments in this series

conducted by NBS. These results are in agreement with the earlier

studies. Basic groundwork is provided for additional experiments

and analysis which will form a practical basis for recommending

energy-conserving design Illumination levels that conform to realworld office activities.

Key words: Conspicuity; contrast; energy conservation; illumination;

illumination levels; lighting, suprathreshold seeing;

visibility; vision.

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EQUAL APPARENT CONSPICUITY CONTOURS WITH FIVE-BAR GRATING

STIMULI

INTRODUCTION

The visibility of materials encountered in office work ranges

from barely legible to highly legible. With technological advances in

reproduction and writing implements, e.g., copiers, typewriters,

pens and paper technology, the visual tasks prevalent in offices today

are more legible than they were two or three decades ago. There

are, however, no hard data quantifying the relative occurrence of

tasks at various levels of difficulty.

For the designer, the problem faced is: "What illumination

level should I recommend for lighting that will be efficient, yet

provide good seeing for the tasks to be performed?". To conclude

that, "I will recommend the lighting level required for the least

legible task, since it follows that all other tasks with higher

legibility will have increased visibility" may be erroneous.

Arguments of this type are based on popular notions (e.g., more light,

better sight) and are verified in the laboratory only for threshold

tasks (e.g., barely seeing a gap in a circle or detecting a spot

of light) . These types of visual tasks are not usually encountered

in office work. Workers would not tolerate conditions in which they

had to deal with just barely legible materials on a sustained basis,

unless the nature of the task absolutely required it. Instead, the

lighting system and task parameters should permit the worker to read

the materials without any undue difficulty. The foremost information

the designer needs in specifying a lighting system is: considering the

activity and the kind of tasks to be performed in the space, what

1
illuminance levels will enable the worker to comfortably perform

these tasks?

The following study is one in a series investigating the effect

of light levels on "goodness of seeing" for threshold and suprathreshold

tasks

BACKGROUND

Studies conducted to date indicate that when the required

response is, "I can just barely see the object" (threshold task), the

form of the function obtained by plotting contrast against luminance

is different from that obtained when the response is, "I can see the

object, but it is easier to see, that is, it has better contrast,

under luminance level X than Itiminance level Y" (suprathreshold task).

Studies have been conducted with both letters (1) and sinusoidal and

square-wave gratings (2) . Both of these studies indicate that the

forms of the function at threshold and suprathreshold levels are

significantly different. For both types of stimuli, the form of the

function near threshold levels agrees with that obtained in classical

threshold studies. As luminance is increased, the contrast required to

detect the presence of a target or the minimum separation between two

lines decreases monotonically . That is, task visibility increases

as luminance is increased. But on tasks for which detection is not

a problem, i.e., in which the presence of the detail is definitely

established, the form of the function differs significantly from

that found at threshold levels. The suprathreshold data indicate that

as luminance is increased, the degree of contrast required to

maintain equality of apparent contrast decreases initially with

increases in luminance, but that further increases in luminance

2
require increases in contrast to maintain goodness of seeing.

The relevance of these findings to lighting design is obvious; the

popular notion of "more light, better sight" is valid for materials

with poor legibility, but not for good or medium legibility visual

tasks. In fact, for these suprathreshold visual tasks, more light

can mean less sight, that is, increases in Iviminance can result in a

loss of ease of seeing.

The studies described above involved a total of six subjects:

four in the study using letters and two for the gratings studies.

All six were experienced in visual psychophysical experiments . The

following experiment was conducted to obtain data from a larger

number of subjects, most of whom were inexperienced in psychophysics.

The lighting system and targets were different from those previously

used, but the procedure was the same in all important respects.

FIVE-BAR GRATING PATTERN EXPERIMENT

SUBJECTS

Fifty subjects participated in this experiment, all of whom

were affiliated with the University of Virginia. Thirty were

undergraduates, nineteen graduate students. All had little or no

experience in visual psychophysical experiments. The one remaining

subject was an experienced participant in vision experiments.

STIMULI

The stimuli were photographic reproductions of the NBS Microcopy

Test Chart 1963A magnified two times. These charts are composed of

groups of alternating dark and light bars of various bar widths and

are used primarily for quality control and legibility evaluation of

3
micrographic systems. Each group consisted of five dark and four

light bars (Fig. 1). Two sets of charts were made, the background

reflectance for the dark bars on one set being twice that of the

other. The background reflectance was the same for all charts in a

set. Each set was composed of charts which differed in contrast in

steps of approximately 0.02, where contrast is defined as;

Contrast = (L^ - Lj^)/L^,

and the subscripts B and D stand for background and detail,

respectively. Three bar widths, corresponding to 6.0, 3.8, and

2.4 minutes of visual angle, were used in the study; the contrast

values for the charts used for each of these widths are shown in

Figs. 2 and 3, for the high and low reflectance background sets,

respectively. The 3.8 min. values have been displaced by 0.1 unit

on the ordinate axis and the 2.4 min. values are 0.2 units higher.

The contrast for each chart was measured with a microphotometer at

the viewing angle used in the experiment (25 degrees from normal to

the chart) and with the same lighting system used in the experiment.

A test chart holder allowed only a 5 cm (2 in) square portion of each test

chart to be exposed. The exposed portion of each test chart was

surrounded by a cover with a reflectance that was an average of the

backgrounds of the two sets of charts. The openings exposing the

test chart details were separated by 22.5 degrees from center to

center.

4
1.25 1.4 1.6

Figure 1. NBS Microcopy Test Chart.
CONTRAST

TARGET NUMBER

Figure 2. Contrasts of high reflectance background tharts. Values for

3.8 min. and 2.4 min. curves have been displaced upward by

0.1 and 0.2 units, respectively, on the vertical axis.

6
CONTRAST

Figure 3. Contrasts of low reflectance background charts. Values for

3.8 min. and 2.4 min. curves have been displaced upward by

0.1 and 0.2 units, respectively, on' the vertical axis.

7
LIGHTING SYSTEM

A drawing of the experimental booth is presented in Fig. 4. The

booth was 1.8 m (6 ft) across and 1.5 m (5 ft) deep, with the lamps

located 2.1m (7 ft) above the floor. The task surface was 75 cm

(30 in) above the floor. A white, translucent plexiglass cast sheet,

6.4 mm (1/4 in) thick with a matte finish on one side, was installed

21 cm (8 in) below the lamps. The lamps were standard 40w cool white

rapid start lamps spaced 7.6 cm (3 in) apart. The booth was enclosed

by a white cloth curtain. The illuminance in the booth could be

continuously varied using a solid-state dimming system. No change

in color temperature occurred when dimming the lamps.

PROCEDURE

The observer (0) was seated and the chin and forehead rest

adjusted so that the target was viewed at a distance of 38 cm (15 in)

and at an angle of 25 degrees from the normal to the task surface.

Two charts, one from each set, were placed in the chart holder, the

angular separation between the test bars on the two charts being

22.5 degrees. The observer was instructed to look at the center

bar on the comparison (high reflectance background) chart and compare

its apparent contrast with that of the corresponding bar on the test

(low reflectance background) chart. If 0 thought that the bar on the

test chart had more contrast than the bar on the comparison chart, he

asked the experimenter for a test chart with less contrast. If, on

the other hand, 0 thought that the bar on the test chart had less

contrast than the bar on the comparison, he asked for a test chart

with more contrast. The process continued until the observer

perceived the bars on the two charts as being equal in apparent contrast.

8
SCENT

9

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Three such matches were made, and the median contrast of the test

chart chosen in these matches was recorded. The illumination level

was then halved, and the contrast of the test chart chosen in these

matches was recorded. The illumination level was then halved, and

the comparison chart was replaced by one of the same physical contrast

as the median test chart recorded above (thus each new comparison chart

was determined by the observer’s contrast matches on the previous

set of trials). The observer made three more matches, and a new standard

was determined. This process was repeated until 0 completed the

2 2

range of luminances for the experiment, 700 cd/m to 5.5 cd/m .

The instructions to the subjects are given in Appendix A.

Twelve experimental conditions were used — three target sizes

(6.0, 3.8, and 2,4 min. of visual angle, corresponding to chart

numbers 1.4, 2.0, and 3.2, respectively) at four initial contrast

levels (0.7, 0.5, 0.3, and 0.15). The order of these conditions

was randomized for each subject, with one exception. The first

session was balanced across subjects so that an equal number would

begin at each of the twelve conditions. Half of the subjects had the

comparison chart placed on their right, while the other half had it

placed on their left.

All subjects first did one practice run at 0.5 contrast,

6 min. target size, which consisted of five matches at each luminance

2 level. The initial luminance level was 700 cd/m and the final level

2 was 5.5 cd/m , but a reverse run condition was also included in which

the comparison and test charts were switched, and the luminance level

progressed from lowest to highest.

10
RESULTS

Figs. 5-7 present a summary of the data. Each curve is an equal

apparent contrast contour, that is, all of the connected points were

perceived to be equal in contrast at the different levels of illumination

The four symbols represent different starting contrast levels at

2

700 cd/m : open circle = 0.70, square = 0.50, triangle = 0.30, and

hexagon = 0.15. Each point on a curve represents the arithmetic

average of fifty observers. Figs. 5, 6, and 7 represent the results

for the different bar widths — 6.0, 3.8, and 2.4 min., respectively.

The functions are similar for these three figures. In general,

the two higher starting contrasts (0.70 and 0.50) have a positive

slope, whereas the two lower starting contrast levels (0.30 and 0.15)

have a negative slope. In visibility terms, for the two lowest sets

of curves, as we increase lumin2ince, the contrast required for the

bars to be subjectively equal decreases monotonically . But the

apparent contrast contours for the two higher levels are the opposite.

The contrast required for the bars to be subjectively equal increases

monotonically as luminance is increased.

DISCUSSION

Figures 8 and 9 compare the results of the five-bar grating

pattern, experiment with those of the earlier grating study (2). The

solid lines in Figs. 8 and 9 are the equal apparent contrast contours

obtained when the stimulus was a square-wave grating pattern with a

bar width of 7.7 min. Each figure gives the results for a single

observer. The dashed lines connect the points shown in Fig. 5, and were

11
CONTRAST

II

LOG LUMINANCE (CANDELAS/m^

)

Figure 5. Equal apparent contrast contours for five-bar grating pattern

stimuli. Bar width = 6.0 min. of visual angle. Data points are averages for fifty observers.

12
CONTRAST

0.8

Figure 6. Equal apparent contrast contours for five-bar grating pattern

stimuli. Bar width = 3.8 min. of visual angle. Data points

are averages for fifty observers.

13
CONTRAST

LOG LUMINANCE |CANDELAS/n|2|

Figure 7. Equal apparent contrast contours for five-bar grating

pattern stimuli. Bar width = 2.4 min. of visual angle.

Data points are averages for fifty observers.

14
1.0

0.9

0.8

0.7

0.6 -

0.5

0.4

0.3

0.2

0.1

0.0 1

-1.0 0.0 1.0 2.0

LOG LUMINANCE |CANDELAS/m2)

3.0

Figure 8, Comparison of equal apparent contrast contours for five-bar

and square-wave grating stimuli. Bar width = 6.0 and 7.7 min.

of visual angle for five-bar and square-wave gratings,

respectively. Data points for five-bar grating curves are averages for fifty observers. Data points for square-wave

grating curves are for a single observer (GY)

.

15
CONTRAST

Figure 9. Comparison of equal apparent contrast contours for five-bar

and square-wave grating stimuli. Bar width =6.0 and 7.7 min.

of visual angle for five-bar and square-wave gratings,

respectively. Data points for five-bar grating curves are averages for fifty observers. Data points for square—wave

grating curves are for a single observer (YK)

.

16
obtained using the five-bar stimulus with line widths of 6.0 min. The

curves all show that as the contrast level of the equal apparent

contrast contours Increases, the slopes fan out, that is, we start

with a negative slope and end with a positive slope. Both sets of

curves thus demonstrate that for tasks of low contrast, the contrast

required to give a perception of equal contrast monotonically

decreases as luminance is increased. However, for higher contrast

levels (more visible tasks) , increasing luminance beyond some value

results in a decrease in contrast sensitivity; the actual contrast must

be Increased at higher luminances to give a perception of equal contrast.

Although the results for the five-bar chart do not show a minimum,

the results for the square-wave gratings suggest that with further

decreases in luminance, the two upper dashed curves in Figs. 8 and 9

will probably reverse, i.e., a minimum will occur.

Figure 10 compares the results of the five-bar grating pattern

study with those of the study using letters (1). The solid curves

in Fig. 10 are the results of the experiment using letters with stroke

widths of 6.5 min. as the task stimulus. The dashed curves are the

results from the five-bar grating experiment given in Fig. 5. The

test stimuli are different, one being letters and the other, straight

lines. But again, the differences between the curves as we go higher

up the contrast scale are the same for both sets, and there is a fanning

out of the curves as seen in Figs. 8 and 9.

17
CONTRAST

1.0 r0.9 -

0.8 -

0.7 -

0.6 -

0.5 -

0.4 -

0.3 -

0.2 -

0.1 -

0.0 _

Figure

•—• LETTERS

0--.HO FIVE-BAR GRATING

0----o

o>.

-L

- 1.0

-J I L.

0.0 1.0 2.0

LOG LUMINANCE (CANDELAS/m^j

-L.

3.0

10. Comparison of equal apparent contrast contours for five-bar

grating and letter stimuli. Bar and stroke widths = 6.0 and

6,5 min. of visual angle, respectively, for gratings and letters.

Data points are averages for fifty observers for gratings and

four observers for letters.

18
A second study using the letter stimuli was also conducted in

conjunction with the present study, using the same procedure. The

results are given in Figs. 11, 12, and 13, for stroke widths of 6.5,

4.0, and 3.2 min. of visual angle, respectively. Each data point is

the arithmetic average for nine subjects. The results for all three

stroke widths are quite similar. They are also similar to the results

obtained with the five-bar charts, although the fanning out of the

lines is not as pronounced as it is for the five-bar stimuli.

The results of both of the grating studies and both of the

letter studies indicate that the function changes from a "more light,

better sight" one to a "more light, less sight" curve as the contrast

of the task increases. For low visibility tasks, increasing luminance

results in increased "goodness of seeing", but for tasks with contrasts

greater than approximately 0.4, increasing luminance does not enhance

visibility. More seriously, a loss in clarity of detail occurs as

luminance is increased for these suprathreshold tasks.

Four sets of data utilizing the apparent equal contrast contour

technique have been presented and discussed. There are clear indications

that a single function cannot qualitatively treat visual tasks that

are at or near threshold levels and nonthreshold tasks. The first

letter study utilizing four subjects indicates that for tasks above

approximately 0.4 contrast the optimum level is approximately

2

50 cd/m (15 ftL) . The data from the grating studies and the second

letter study, however, indicate a lower optimum luminance level.

Although no definite value can be stated at this time, it appears to be

significantly less than those being recommended by the lES in the 5th

edition of their handbook.

19
CONTRAST

0.8

0.0 1.0 2.0 3.0

LOG LUMINANCE (CANDELAS/m^)

Figure 11. Equal apparent contrast contours for letter stimuli. Stroke

width =6.5 min. of visual angle. Data points are averages

for nine observers.

20
CONTRAST

0.8

0.0 1.0 2.0 3.0

LOG LUMINANCE (CANDELAS/m ^

)

Figure 12. Equal apparent contrast contours for letter stimuli. Stroke

width = 4.0 min. of visual angle. Data points are averages

for nine observers.

21
CONTRAST

LOG LUMINANCE (CANDELAS/m^

Figure 13. Equal apparent contrast contours for letter stimuli. Stroke

width = 3.2 min. of visual angle. Data points are averages

for nine observers.

i

22
The tendency of workers to evaluate the lighting system by how

bright the environment is, rather than by how well they can see,

must be considered in lighting level recommendations. But it is not

valid to use preferred light levels as the criterion for lighting

quality, as preference studies conducted to date have shown that this

will result in extraordinarily high levels. The assessment should be

made by an open-ended questioning of the workers, that is, the criterion

should be complaints received, and not what the workers say they prefer.

No indication should be given that it is the light levels which are

being investigated. If more than 10% of the workers complain that

the light level is too low, it may be considered unacceptable.

Since the levels that most people prefer are significantly above

the optimum levels for visual performance, the optimum levels determined

from laboratory studies should be used together with the open-ended

questionnaires to optimize physiological and psychological aspects of

illumination requirements for visual task performance. This compromise may

be a level higher than the laboratory determined optimum (beyond which

loss of visibility occurs), but lower than the preferred level, and

should not lead to rejection of the lighting system as intolerable.

The equal apparent contrast or equal visibility contours describe

the effect of luminance on the apparent contrast of the task, but do not

provide the information required to determine the apparent contrast

that should serve as the standard visibility criterion function. That

is, what level of visibility or ease of seeing should be recommended

for visual task performance? Obviously, a threshold or near-threshold

level criterion will be unsatisfactory, as it assumes working under

difficult visual conditions, unless it is only encountered occasionally

23
or is inherent in the task. Conversely, to set the visibility

criterion at a high level, although it may be preferable from the

worker's point of view, may make meeting the criterion impossible

or difficult at best because of economic reasons.

One method for determining what visibility level should be

recommended is to experimentally determine the criterion level that

will be acceptable to most workers, e.g., 90%. To this end, a

preliminary study was conducted using the subjects, lighting system,

and stimuli from the Microcopy test chart experiment. At a given

luminance level, task contrast was varied and observers were asked to

choose the contrast level which they felt would be "just acceptable"

for sustained work (reading for four hours) . They were also asked to

choose the level they felt would be "definitely acceptable". The

highest just acceptable contrast level would then serve as the

lower boundary and the lowest definitely acceptable level as the

upper boundary of the region comprising contrast values that were

neither too good nor too poor for sustained visual task performance.

That is, assume all observers have chosen their just good enough and

definitely good enough contrast levels, and that the spread of the

data points is such that all just good enough points lie between a

lower level A and an upper level B, and that all definitely good

enough points lie between lower level C and upper level D. Further

assume that level C is higher in contrast than level B. It is then

possible to say that an acceptable contrast level for sustained visual

work lies between contrast levels B and C.

24
i!

l:

r

ii

I The means and standard deviations for the acceptability experiments

I are given in Table 1. If we assume that the extreme upper and lower

10% of the subjects, respectively, were either overly demanding or

understating needs, for reasons other than visual goodness of the

I task, the range of values remaining will be the mean plus and

minus 1.28 times the standard deviation. By making this a one-tailed

test, mean plus 1.28 standard deviations for the just acceptable and

mean minus 1.28 standard deviations for the definitely, we include

90% of the population. The region where the just and definitely

acceptable bars do not overlap would represent contrast values that

are acceptable, that is, not too good nor what would be called a poor

or low visibility task for 90% of the sampled population.'

The results are presented in Figs. 14-16. None of the pairs of

bars presented in these figures show a nonoverlap region. These

results indicate that there are large differences among observers'

evaluations of "goodness of task" required for sustained visual work.

What is considered "definitely acceptable" by some observers may be

considered less than "just acceptable" by others. The large overlapping

of just and definitely acceptable goodness of seeing between observers

may be due to psychological (subjective) factors that differ from observer

to observer. Rather than relying on impression of acceptability, a

measure more directly assessing contrast sensitivity may lead to less

variability between subjects.

25
Mean

and

Standard

Deviation

(in

parenthesis)

of

Task

Contrasts

for

Five-bar

Grating

Stimuli

Perceived
CONTRAST

Figure 14. Ranges of contrasts judged "just acceptable" and "definite!

v

acceptable" for sustained reading. Five-bar grating pattern

stimuli at luminance of 700 candelas/m^.

27
CONTRAST

BAR WIDTH (MINUTES OF VISUAL ANGLE)

Figure 15. Ranges of contrasts judged "just acceptable" and "definitely

acceptable" for sustained reading. Five-bar grating pattern

stimuli at luminance of 88 candelas/m^.

28
CONTRAST

I Figure 16. Ranges of contrasts judged "just acceptable" and "definitely

acceptable" for sustained reading. Five-bar grating pattern

stimuli at luminance of 11 candelas/m^.

29
We are proposing to use a method in which response variability

within observers as opposed to between observers is used as the

indicator of goodness of seeing. It is known that response variability

increases as discriminability decreases. For example, in matching

two fields so that they are identical in all respects, the variability

in the matches increases as luminance and/or angular subtense is

decreased (3). At a given luminance level, matches will be made

between two fields for equality in contrast. The expectation is

that the variability will be large at low contrast levels, and that

variability of response will decrease as contrast is increased. A

variance vs. contrast plot may give a function with a natural division

between the lower and upper half. This is an empirical question,

and will have to await further experimental studies.

r
References

1. Yonemura, G. T. , Benson, W. M. , and Tibbott, R. L. , "Levels of

Illumination and Legibility", NBS Interagency Report 77-1306,

1977. National Technical Information Service (NTIS)

,

Springfield, Virginia 22151.

2. Yonemura, G. T. and Kohayakawa, Y., "A New Look at the Research

Basis for Lighting Level Recommendations", NBS Building Science

Series 82, 1976. U.S. Government Printing Office, Washington, D.C.

20402, SD Cat. No. C13. 20/2:82.

3. Yonemura, G. T. and Kasuya, M. , "Color Discrimination under

Reduced Angular Subtense and Lviminance", J. Opt. Soc. Am.

^

(2), 131-135, 1969.

31
APPENDIX A

INSTRUCTIONS

THIS IS AN EXPERIMENT ON CONTRAST, THAT IS, HOW WELL DETAILS STAND

OUT AGAINST THEIR BACKGROUNDS. YOU WILL BE SHOWN TWO CHARTS, SIDE BY

SIDE, THAT ARE DIFFERENT. YOUR TASK WILL BE TO REPLACE ONE OF THESE

CHARTS UNTIL YOU FIND ONE WHICH HAS THE SAME CONTRAST AS THE OTHER

CHART.

(Experimenter puts in card #1, 1.4 size, on subject's left and #2

on subject's right)

NOW LOOK AT THE MIDDLE HORIZONTAL DARK BAR OF THE 1.4 GROUP ON

THE LEFT CHART. THEN LOOK AT THE SAME BAR ON THE RIGHT CHART. NOTICE

THAT THE BAR ON THE RIGHT CHART HAS MORE CONTRAST, THAT IS, IT STANDS

OUT FROM ITS BACKGROUND BETTER THAN THE BAR ON THE LEFT CHART. WHENEVER

THIS HAPPENS, SAY "LESS" AND I WILL REPLACE THE RIGHT CHART WITH ONE

THAT HAS LESS CONTRAST.

ON THE OTHER HAND, THE RIGHT CHART MAY LOOK MORE LIKE THIS.

(Experimenter takes out card #2, puts in #3)

NOW THE MIDDLE BAR ON THE RIGHT CHART DOES NOT STAND OUT FROM

ITS BACKGROUND AS WELL AS THE BAR ON THE LEFT CHART DOES. WHEN THIS

HAPPENS, SAY "MORE" AND I WILL REPLACE THE RIGHT CHART WITH ONE THAT

HAS MORE CONTRAST.

(Experimenter takes out card #3, puts in #4)

HERE IS A CHART WHOSE CONTRAST IS CLOSER TO THAT OF THE OTHER

CHART. IF IT HAD A LITTLE MORE OR LESS CONTRAST, IT MIGHT BE EQUAL

IN CONTRAST TO THE OTHER CHART. WHEN YOU ARE SATISFIED THAT THE TWO

BARS HAVE THE SAME CONTRAST, SAY "EQUAL".

32
HERE ARE 2 CARDS THAT HAVE THE SAME CONTRAST. NOTICE THAT THEY

DIFFER IN DARKNESS AS WELL. WE WANT YOU TO MAKE YOUR MATCHES ON THE

BASIS OF HOW WELL THE ITEM STANDS OUT FROM THE BACKGROUND, ON THE

BASIS OF DARKNESS.

YOU SHOULD ATTEND TO THE RATIO OF EACH CARD. NOT THE TOTAL DARKNESS.

THERE IS NO TIME LIMIT NOR RESTRICTION ON THE NUMBER OF CHARTS

YOU MAY ASK FOR. YOU MAY LOOK AT THE SAME CHART MORE THAN ONCE. YOU

SHOULD LOOK AT CHARTS WHICH ARE BOTH HIGHER AND LOWER IN CONTRAST THAN

THE ONE YOU ULTIMATELY SELECT. DOUBLE-CHECK YOUR SELECTION BEFORE YOU

SAY "EQUAL”. USE MORE TIME FOR YOUR FINAL SELECTION.

DO YOU HAVE ANY QUESTIONS?

LET'S TRY AN EXAMPLE.

(Experimenter replaces cards //I and #4 with randomly selected

light and dark background cards from the 1.4 series. Subject makes

a match.)

33
NB^114A (REV. «-7a)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBSIR 79-1925

4. TITLE AND SUBTITLE

Equal Apparent Conspicuity Contours with Five-Bar Grating

Stimuli

5. Publication Date May 1980

7. AUTHOR(S)

Yonemura, Gary T. , Rinalducci, Edward L., Tibbott, Robert L.

,

and Fogelgren, Linda A.

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

M»(i/s^^?>"r5bE/NBC

lAG No. EA-77-A-01-6010

12. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS fStreer, City, stato, ZIP)

Architectural and Engineering Systems Branch

Division of Building and Community Systems

Office of the Assistant Secretary

Conservation and Solar Applications

Department of Energy. Washington. D .C. 20545

13. Type of Report & Period Covered Final

15. SUPPLEMENTARY NOTES

This report summarizes the results of laboratory research related to task lighting

conducted by the University of Virginia, Dept, of Psychology, through a grant to the

16« ABSTRACT (A 200*word or toaa factual aummary of moat aignfficant information. If document inetudea a significant bibliography or

literature survey, mention it here,) The report discusses the results of , laboratory studies on equal conspicuity (contrast)

contours using as the test stimuli five-bar grating patterns, with the results of

other experiments in this series conducted by NBS. These results are in agreement

with the earlier studies. Basic groundwork is provided for additional experiments

and analysis which will form a practical basis for recommending energy-conserving

design illumination levels that conform to real-world office activities.

17* KEY WORDS faix to twelve entries; alphabetical order; capitalize only the first tetter of the first key word unless a proper name;

separated by aemicolona)

Conspicuity; contrast; energy conservation; illumination; illumination levels;

lighting; suprathreshold seeing; visibility; vision.

19. SECURITY CLASS 21. NO. OF

(THIS REPORT) PRINTED PAGES

UNCLASSIFIED x

37

20. SECURITY CLASS 22. Price (THIS PAGE)

1 $6.00

UNCLASSIFIED x

18. AVAILABILITY [x] Unlimited

I I For Official Distribution. Do Not Release to NTIS

I 1 Order From Sup. of Doc., U.S. Government Printing Office, Washington, DC

20402, SD Stock No. SN003-003- Pn Order From National Technical Information Service (NTIS), Springfield, VA. 22161 USCOMM-C3C

i

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