An Optimal Text/Background Color
Combination of LED Information Boards
for Visibility Improvement
Based on Psychological Measurements
Aya Shiraiwa1 , Eriko Aiba1,2,3 , Takayuki Shimotomai4 , Hiroya Inome1 ,and Noriko Nagata1
1

Graduate School of Science and Technology, Kwansei Gakuin University, 2-1
Gakuen, Sanda, Hyogo 669-1337, Japan{shiraiwa.aya,nagata}@kwansei.ac.jp
2
National Institute of Advanced Industrial Science and Technology, 1-8-31
Midorigaoka, Ikeda, Osaka 563-8577, Japan
3
Research Fellow of the Japan Society for the Promotion of Scienceaiba.eriko@aist.go.jp
4Brain Science Institute, Tamagawa University, 6-1-1 Tamagawa-gakuen, Machida,
Tokyo 194-8610, Japanshimotomai@lab.tamagawa.ac.jp

Abstract. In this study, conspicuity and readability of the text onlight-emitting diode (LED) information boards were evaluated by psychological experiments, and the inﬂuences of color combinations of text
/ background, luminance, and shadow were evaluated quantitatively. In
recent years, LED boards have been able to display full-color images,
and they have many functions to highlight text. Therefore, it is assumed
that the LED board ability to function may be reduced depending on
the way it is used. We investigated the relationship of color combinations of text and background, luminance, and shadow to conspicuity andreadability to evaluate ease and eﬃciency of information communication
via the LED board. We found that (1) the size of the area with high luminance aﬀected conspicuity, (2) the diﬀerence of luminance of the partadjacent to the text/background aﬀected readability, and (3) shadow affected both conspicuity and readability. Furthermore, trade-oﬀ between
them was conﬁrmed.
Keywords: visibility, LED, color combination, Scheﬀe’s paired comparison.

1

Introduction

In recent years, not only for lighting and television, but also for electronic displays such as various traﬃc signs and displays, the light-emitting diode (LED)
has been well-used. In addition to its major characteristics, such as compact
S. Tominaga, R. Schettini, and A. Trémeau (Eds.): CCIW 2013, LNCS 7786, pp. 119–132, 2013.
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size, energy savings, and long life, LED ability to display full color and high luminance intensity has improved, so the LED is being used for various purposes.
LEDs have been used widely, especially as electronic displays, because of theirability to display in full color including white color, show blinking or scrolling
text, and display text or pictures easily.
The object of this study is the information indicator LED board in which
LEDs are placed in a dot-matrix conﬁguration, such as the LED traﬃc sign. We
investigated the visibility of the LED boards.
Visibility is deﬁned as the degree of conspicuousness of the objects [1], [2],[3]. When information is displayed by using LED boards, not only the LED
board itself needs to be noticeable, but the contents also need to be understood.
Moreover, because LED boards have various functions, it is possible to reduce
the original LED boardfs ability to convey information depending on the way it
is used. Therefore, the relationship of the optimal color combination of text andbackground, luminance intensity, and shadow needs to be arranged properly sothat LED board users are able to send information easily and eﬃciently.
Regarding conspicuity and readability of the color combination of text andbackground, many previous studies have been conducted using a cathode ray
tube (CRT) or liquid crystal display (LCD) [4], [5], [6], [7]. Moreover, there arevarious studies; such as the impact of web page text/background color combinations on retention of memory and readability and the eﬀects of text/backgroundcolor combination on readability of electric paper and LCD in discriminating
performance for young and elderly [3], [8], [9]. The one previous study using
LEDs examined the eﬀect of the color combination of text/background on human comfort and readability with LED display computers [10]. However, there
is no study concerning LED boards on which LEDs are placed in a dot-matrix
conﬁguration, such as the LED traﬃc sign. Furthermore, even though shadow
text is often used to emphasize the text or sentence on LCD displays, there are
only a few studies considering conspicuity and readability with shadow text.
Considering previous studies, not using CRT, LCD, or LED display computers,
but using LED boards, there is a possibility that characteristic eﬀects of LED
on color combinations of text and background may appear.
Therefore, the purpose of this study is to quantify the factor of visibility ofcolor combinations of text/background on LED boards, that is, conspicuity andreadability.
In this study, we used LED boards and changed color combinations of text
and background each time. Then, we evaluated the visibility based on a paired
comparison. At ﬁrst, we used chromatic color and arranged the experiment considering luminance; then evaluation of conspicuity and readability was conductedby a psychological scale. Next, the experiment to add achromatic colored shadow
to the text was conducted, and we evaluated the inﬂuence of the stereoscopic
eﬀect added by shadow text for conspicuity and readability. Furthermore, fromthe ﬁndings of Experiment 1, we evaluated visibility when diﬀerence of luminance of chromatic color was signiﬁcant, not considering the luminance. Lastly,
integrating the result of these experiments, it was determined that conspicuity

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and readability have a trade-oﬀ relationship in color combinations of text andbackground. It was also determined that visibility was improved by diﬀerence ofluminance or by adding shadow on the text.

2

Experiment 1: The Influence of the Hue under theCondition of Same Luminance

In Experiment 1, we investigated the inﬂuence of the diﬀerence of the hue on
conspicuity and readability, under the condition of same luminance. Previous
studies have demonstrated that the diﬀerence between the colors of text andbackground aﬀects conspicuity and readability. However, various opinions about
the inﬂuence of the hue on the color combination have not yet been conﬁrmed.
Therefore, in Experiment 1, the eﬀect of hue under the condition of same luminance was investigated.
2.1

MethodParticipants. 116 observers (97 male and 19 female; average age: 20.9 years
old) participated in Experiment 1.
Apparatus. The text stimuli were shown on the information indicator (LEDboard) with LEDs placed as a dot-matrix display. The LED board was placed
positioned 180 cm from the ﬂoor. The experiment was arranged in the lectureroom at Kwansei Gakuin University. The participants took seats between nine
lines of right and left and 13 lines of anteroposterior. Each participant’s seat
location was recorded. The LED board, except for the area of stimuli indication,
was covered with a black cloth. The luminous intensity of the LED board was
905 lux, under the condition with lights on and curtains of the lecture room
closed.
Stimuli. We used the text letter “E” as the stimulus, displayed in red, green,
blue, and yellow. The colors of the background were red, green, blue, yellow,
black, and white. Twenty combinations of text and background color were used.
The red, green, and yellow used in the experiment were not pure color, because
each luminance of the color was standardized based on the luminance of blue,
which was the darkest luminance among of them.
Procedure. We showed four stimuli of “E” with diﬀerent color combinations oftexts and backgrounds at the same time on an LED board. Exposure duration
for the stimuli was 15 seconds at ﬁve-second intervals, with each exposure duration and interval counted as one trial; we repeated the stimulus for 78 trials.
Furthermore, we considered the inﬂuence of the luminance by using black andwhite, which were of a diﬀerent luminous intensity from the chromatic color.
From the ﬁrst trial to the 65th trial, all patterns of color combination stimuli
were shown at random, then, from the 66th trial to 78th trial, we only showed
the color combination stimuli that did not include black and white.

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Task. Regarding conspicuity and readability of stimuli presented to the participants, they were instructed to indicate a ranking of readability from No. 1 toNo. 4 on a questionnaire for each trial.
Analysis. The data were analyzed using Scheﬀe’s paired comparison method(modiﬁed Haga’s method). Participants arranged the ranking for four patternsof stimuli that were presented to participants at the same time. We made thesefour rankings paired, two stimuli each. Then, we analyzed as a total of six pairs.
Although the correlation with these results and the seat location was also veriﬁes,
it was conﬁrmed that the seat location did not aﬀect the results.
2.2

Results

The results of Experiment 1 are shown in Fig. 1 and 2. Fig. 1 indicated theconspicuity of stimuli patterns, and Fig. 2 was for readability of stimuli patterns.
The vertical axis indicates the evaluation value for conspicuity and readability(z-score; gap value from the average value for each data), and the horizontal axis
showed that a negative value indicated a better evaluation.
From the results of Experiment 1, the characteristic results were obtained
concerning both conspicuity and readability for the color combination stimuli
patterns with the black/white backgrounds. For conspicuity, all patterns with awhite background obtained higher ratings. Almost all patterns with a black background obtained a lower rating. Besides the white background, the red tended
to receive a better rating. For readability, the stimuli patterns with black orwhite background tended to receive higher rating. We could not ﬁnd a particular tendency for the color combination patterns combining chromatic colors.
Furthermore, there was no major diﬀerence between the 66th trial and the 78th
trial, which tested only color combination patterns without black and white
being a diﬀerent luminance from the chromatic color. Therefore, we were notable to conﬁrm the inﬂuence of the diﬀerence of hue (combination of chromaticcolors).

3

Experiment 2: The Influence of Shadow Text

We investigated the eﬀect of shadow text, which increases the stereoscopic eﬀect.
We investigated whether or not this stereoscopic eﬀect aﬀects conspicuity andreadability. Contrary to Experiment 1, we used only achromatic color in thisexperiment so that we could focus on only the diﬀerence of luminance to investigate conspicuity and readability in this experiment. Furthermore, we considered
the stereoscopic eﬀect obtained by the luminance of the color of the shadows, orby existence or non-existence of the shadow.
3.1

MethodParticipants. 18 observers (15 male and three female; average age: 22.2 years
old) participated in Experiment 2.

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Fig. 1. Psychological measure for conspicuity under the condition of same luminance:
First letter is text color and second letter is background color. R, Red; G, Green; B,
Blue; Y, Yellow; K, Black; W, White.

Fig. 2. Psychological measure for readability under the condition of same luminance:
First letter is text color and second letter is background color. R, Red; G, Green; B,
Blue; Y, Yellow; K, Black; W, White.

Apparatus. The apparatus is the same as in Experiment 1.
Stimuli. Stimuli were presented on an LED board in the same manner as Experiment 1. The text of gEh was presented as in Experiment 1. The colors of thetext and the background were black, white, and gray. The colors of the shadow
were black, white, and gray. There were two patterns of stimuli presented: “withshadow” and “without shadow.” The 12 patterns of stimuli presented used combinations of diﬀerent colors for text, background, and shadow.
Procedure. We presented two patterns of stimuli at the same time. Exposure duration and intervals of the stimuli were the same as the procedure of

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Experiment 1. Participants observed stimuli during 66 trials. A trial consistedof a 15-second exposure duration and a ﬁve-second interval.
Task. Concerning three items – “conspicuity,” “readability,” and “stereoscopic
eﬀect” of indicated stimuli – the participants were instructed to choose the betterone from each presented paired of stimuli, and to ﬁll out a six-step evaluationfor each presented pair in a questionnaire.
Analysis. As in Experiment 1, the data were analyzed using Scheﬀe’s paired
comparison method (modiﬁed Haga’s method).
3.2

Results

The results of Experiment 2 are shown in Fig. 3, 4, and 5. Fig. 3 indicates theconspicuity of stimuli patterns, Fig. 4 shows readability of stimuli patterns, andFig. 5 shows stereoscopic eﬀect. The vertical axes of Fig. 3– 5 were for evaluation
value of conspicuity, readability, and stereoscopic eﬀect (z-score). The horizontal
axis indicated color combination patterns of presented stimuli. In the verticalaxis a negative value indicates a better evaluation.
For conspicuity, as in the results of Experiment 1, the white backgroundobtained the highest evaluation. Color combination patterns in order of obtaining high evaluation ranked 1) white background, 2) white text, and 3)
white shadow text. Color combination patterns without any white received
the lowest evaluation rating. For readability, larger diﬀerences between color oftext and background or between luminance of color of text and shadow (whiteand black) obtained higher evaluations. Concerning the stereoscopic eﬀect, theblack shadow received the highest evaluation. Poor evaluation was given to text
without shadow.

Fig. 3. Psychological measure for conspicuity under the condition of shadow text: First
letter is text color and last letter is background color. Second letter is shadow colorand “ ” is without shadow. K, Black; W, White; G, Gray.

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Fig. 4. Psychological measure for readability under the condition of shadow text: First
letter is text color and last letter is background color. Second letter is shadow colorand “ ” is without shadow. K, Black; W, White; G, Gray.

Fig. 5. Psychological measure for stereoscopic eﬀect under the condition of shadow
text: First letter is text color and last letter is background color. Second letter isshadow color and “ ” is without shadow. K, Black; W, White; G, Gray.

4

Experiment 3: Influence of Hue without Respect
to Luminance

In Experiment 3, unlike Experiment 1 in which the luminance of color of text
and background were arranged the same, we investigated the color combination
patterns with high evaluations by disregarding the diﬀerence in luminance andusing pure colors. Furthermore, we examined conspicuous and readable color
combination patterns.
4.1

MethodParticipants. 64 observers (54 male and 10 female; average age: 19.4 years old)participated in Experiment 3.

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Apparatus. The apparatus is the same as in Experiment 1.
Stimuli. As in Experiment 1, we presented stimuli on an LED board. The
text of “E” was presented as in Experiment 1. To arrange the diﬀerence ofluminance for the largest possible contrast, we divided the colors into groupsof high luminance and low luminance. The group of high luminance included
white and yellow, and the group of low luminance included black, blue, and red.
The text and background color were from the two diﬀerent luminance groups.
A total of 12 patterns of stimuli were presented. Unlike Experiment 1, we usedpure colors only in Experiment 3.
Procedure. The procedure is the same as in Experiment 2.
Task. For two items, “conspicuity” and “readability” of presented stimuli, theparticipants were instructed to choose the better one from the presented pairedof stimuli, then to ﬁll out a six-step evaluation for each pair in questionnaire.
Analysis. The analysis is the same as in Experiment 2.
4.2

Results

The results of Experiment 3 are shown in Fig. 6 and 7. Fig. 6 indicates theconspicuity of stimuli patterns, and Fig. 7 indicates readability of stimuli patterns. The vertical axes of Fig. 6 and 7 were for evaluation value of conspicuity
and readability (z-score), and the horizontal axis indicated color combination
patterns of presented stimuli. In the vertical axis a negative value indicated thebetter evaluation.
For conspicuity, stimuli patterns using red obtained high evaluation rating,and stimuli patterns using black received low evaluation. Stimuli patterns ofwhite-colored background obtained high evaluations in Experiment 1 and 2;
however, in this experiment, its evaluation changed based on colors of the text.
Conversely, from the view of readability, stimuli patterns using black or blue
received high evaluation. On the other hand, stimuli patterns using red received
low evaluation.
In addition, the evaluation rate of readability added to the evaluation rate ofconspicuity made the value of another characteristic we deﬁned as “visibility,”that is, whether we could see the visual objects clearly or not. Fig. 8 indicatesthe value of visibility. The vertical axis and the horizontal axis of Fig. 8 were thesame as Fig. 6 and 7. For visibility, stimuli patterns using blue obtained highevaluation ratings, and stimuli patterns using black received low evaluations.
Then, analyzing Fig. 8, it was found that stimuli patterns that were highly evaluated tended to be lined up in order of replacing color of text and background.
Therefore, the evaluation rate of visibility tended to be rather ﬁxed by color
combination.
In Experiment 2, the color combination stimuli pattern with Black and White
which had the biggest diﬀerence of luminance obtained good evaluation for readability especially. However, in this experiment, there was the color combination

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stimuli pattern obtained better evaluation than Black and White stimuli pattern of Experiment 2. Therefore, besides diﬀerence of luminance, there could
be existed the parameter which aﬀects readability. According to previous study[11], it has been shown that psychological measure for “favorability” on color
combination aﬀects readability. This was also suggested by the result that thevalue of visibility was lined up in order of each pattern of color combinations.

5

Experiment 4: The Influence of Color Combinationand Shadow Text

In Experiment 4, based on the results from Experiments 1 to 3, we investigatedwhich pattern of color combination was compatible with high conspicuity andreadability among the group of color combination patterns of text and background including shadow text.
5.1

MethodParticipants. 95 observers (73 male and 22 female; average age: 20.7 years old)participated in Experiment 4.
Apparatus. The apparatus is the same as in Experiment 1.
Stimuli. As in Experiment 1, we presented stimuli on an LED board. The text of“E” was presented just like Experiment 1. The text colors were white and yellow;
the background colors were blue and red. Each combination was arranged withor without shadow text (total eight patterns). In addition, total four patterns
were used: black text on white background and white text on black backgroundFig. 6. Psychological measure for conspicuity under the condition without respect toluminance: First letter is text color and second letter is background color. R, Red; B,
Blue; Y, Yellow; K, Black; W, White.

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Fig. 7. Psychological measure for readability under the condition without respect toluminance: First letter is text color and second letter is background color. R, Red; B,
Blue; Y, Yellow; K, Black; W, White.

Fig. 8. Psychological measure for visibility under the condition without respect toluminance: First letter is text color and second letter is background color. R, Red; B,
Blue; Y, Yellow; K, Black; W, White.

as the index of the diﬀerence of luminance; white text on gray background withblack shadow, which received a high evaluation in Experiment 2; and white text
on yellow background with black shadow, which has high luminance for bothcolor of text and background. Total of stimuli patterns was 12 patterns.
Procedure. The procedure is the same as in Experiment 2.
Task. Concerning two items, “conspicuity” and “readability” of indicated stimuli,
the participants were instructed to choose the better one from the presented pairedof stimuli, then to ﬁll out a six-step evaluation for each pair in the questionnaire.
Analysis. The analysis is the same as in Experiment 2.

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129

Results

The results of Experiment 4 are shown in Fig. 9 and 10. Fig. 9 indicated theconspicuity of stimuli patterns, and Fig. 10 was for readability of stimuli patterns.
The vertical axes of Fig. 9 and 10 measure the evaluation value of conspicuity
and readability (z-score), and the horizontal axis indicates color combination
patterns of presented stimuli. In the vertical axis a negative value indicates thebetter evaluation.
Matching the results of Experiment 3, combinations with a red backgroundwere conspicuous but hard to read and the patterns with a black or blue background were easy to read and conspicuous. It was also found that the patternof white text/yellow background/black shadow with highest luminance of text
and background was most conspicuous but the hardest to read. Furthermore,by conducting Experiment 4, we found that the evaluations for both conspicuity
and readability would be higher when shadow was added to the text.
Regarding conspicuity, signiﬁcant diﬀerences at p .01 were found between
text and background in the following paired patterns: white text on yellow background with shadow and yellow text on red background with shadow; yellow on
red with shadow and white on red; white on red with shadow and white on red;white on red and white on blue with shadow; yellow on red and black on white;
white on blue with shadow and yellow on blue; black on white and white ongray with shadow; yellow on blue and white on gray with shadow; white on blue
and white on gray with shadow; white on gray with shadow and white on black.
Then, signiﬁcant diﬀerences of the level of p .05 were found in the following
paired patterns: yellow on blue with shadow and white on blue with shadow.
Regarding readability, signiﬁcant diﬀerences at the level of p .01 were foundin the following paired patterns: yellow text on blue background with shadow andwhite text on blue background with shadow; white on blue with shadow and whiteon blue; white on black and white on blue; white on red with shadow and white on
blue; white on blue and yellow on red with shadow; black on white and white onred; yellow on blue and white on red; white on gray with shadow and white on red;white on red and yellow on red; yellow on red and white on yellow with shadow.
Furthermore, the pattern of white text on red background with black shadow
marked the highest visibility, which was deﬁned as the sum of conspicuity andreadability. We determined that this pattern used the background with conspicuous warm colors and readable white text and black shadow so this pattern wascompatible with conspicuity and readability.

6

Discussion

We investigated the eﬀect of shadow text and the color combination that would
improve conspicuity and readability of presented texts on an LED board. Here,
we discuss the eﬀect inﬂuenced by color combination or shadow text.
First, it was determined that the pattern would be more conspicuous by making the area with high luminance (white or yellow) wider, or by using a warm
color (red). Moreover, it was also determined that the pattern would be more

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Fig. 9. Psychological measure for conspicuity under the condition of considering color
combination and shadow text: First letter is text color and last letter is backgroundcolor. Second letter is shadow color and “ ” is without shadow. R, Red; B, Blue; Y,
Yellow; K, Black; W, White; GY, Gray.

Fig. 10. Psychological measure for readability under the condition of considering color
combination and shadow text: First letter is text color and last letter is backgroundcolor. Second letter is shadow color and “ ” is without shadow. R, Red; B, Blue; Y,
Yellow; K, Black; W, White; GY, Gray.

readable by making the diﬀerence of luminance between color of text and background bigger, or by using a blue or black background. From these, a “trade-oﬀ”
relationship between conspicuity and readability was seen. That is, it could be
not as conspicuous for a color combination that feels good when reading thetext, but if we do not feel good when reading, it could be conspicuous.
In Experiment 1, the luminance of the chromatic color was standardized andpure color was not used. In Experiment 1, characteristic results for conspicuity
were found in the stimuli patterns using black and white, which had a diﬀerenceof luminance compared with chromatic color. However, in Experiment 3 thatluminance was disregarded and pure color was used; the tendency shown in the
results of Experiment 1 was not repeated. From these facts, we found out that an

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inﬂuence stronger than the diﬀerence of luminance could be obtained by using
pure color with the highest saturation in each hue.
Moreover, it was also determined that adding black shadow to the text aﬀectedconspicuity and readability. Regarding the color of the shadow, black gave thestrongest stereoscopic eﬀect. Furthermore, we received some reports from theparticipants that they felt text with gray or white shadow was unnatural because such colors of shadow do not exist in nature. Therefore, it was assumed
that shadow text with a color that exists in nature should be more eﬀective inaccomplishing the stereoscopic eﬀect. Color combination was a “trade-oﬀ” relationship between conspicuity and readability, so it was assumed that the stimuli
pattern with an unnatural shadow color could be conspicuous but not readable.
However, it was actually the case that this pattern received low evaluation forboth conspicuity and readability. Based on this fact, to make the luminance ofthe part adjacent to the text more highlighted, we assumed that using shadow
text would achieve this most eﬀectively only if a natural color pattern were used.
In this study, we used combinations of diﬀerent colors for text and background; however, previous studies determined that there was a color that wasmost suitable for texts [11]. Future studies should address how these ﬁndings
would relate to people’s color perception or visibility.

7

Conclusion

We conducted four experiments in this study for the purpose of improving conspicuity and readability of color combinations of text and background on an
LED board. For conspicuity, it was conﬁrmed that the pattern would be more
conspicuous by making the area with high luminance wider, or by using a warm
color. For readability, it was conﬁrmed that the pattern could be more readable
by increasing the diﬀerence of luminance between the part adjacent to the text
and the background, or by using a particular color combination. Furthermore,by adding black shadow to the text, it was conﬁrmed that both conspicuity andreadability were improved. Then, a “trade-oﬀ” relationship between conspicuity
and readability was suggested.
We evaluated visibility, that is, conspicuity and readability, of the text on an
LED board from the view of color combination. However, many other parametersaﬀect visibility. In future, research should examine the diﬀerence of visibility
depending on where the LED board is placed, the luminance of the LED board,and the diﬀerence in visibility created by the text font.

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