Legibility studies of several EL /electroluminescent/ displays correlate reading time and accuracy with number size, stroke/width ratio, indicia size, pointer width, contrast, ambient illumination, and color background and and contrast. Human factor criteria established on non-EL displays may not apply to EL displays

Mc Lean, M. V.

Miller, G. E.

English

NASA Technical Reports Server

August 1966
	
1.	 Brief 66-10316 
NASA. TECH BRJE.F.. 
NASA Tech Briefs are issued to summarize specific innovations derived from the U. S. space 
program and to encourage their commercial application. Copies are available to the public from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Legibility of Electroluminescent Instrument Panels Investigated 
The problem: 
To .investigate the legibility of EL (electrolumines-
cent) instrument display panels. 
The solution: 
Legibility studies of several EL displays were con-
ducted to correlate reading time and accuracy with 
number size, stroke/width ratio, indicia size, pointer 
width, contrast, ambient illumination, and color back-
ground and contrast. 
How it's done: 
Two indicia and number sizes for a dual, vertical 
EL display were investigated under two levels of ambi-
ent illumination and two contrast conditions. The 
results indicate that speed of reading is affected by 
indicia and number size. For this study, the values of 
0.030 inch for major indicia and 0.020 inch for minor 
indicia, and a stroke width-to-height ratio of 1:8 pro-
duced the best results. This program was not designed, 
however, to find the optimum values, but only to de-
termine if such factors influence legibility. The two 
light levels did not affect performance, but the results 
indicate the research should be continued with illumi-
nation levels well below the minimum 2 foot-candles 
used for this study. Number background contrast in-
fluenced speed of reading and errors made; black 
numerals on a white background were preferred over 
the reverse condition. While the results of the study 
are not conclusive, they indicate that more informa-
tion is required on the perceptual aspects of EL dis-
plays and suggest the direction of subsequent research 
efforts. 
Four EL display configurations were investigated 
for legibility under two levels of ambient illumina-
tion and four color contrast combinations. Results 
indicate that color does not significantly influence
display legibility, that reading time is affected by 
contrast in the favor of black characters on a light 
background, and that the display configuration affects 
reading time and error scores. Circular displays were 
read more rapidly than vertical displays, but with 
greater error. Ambient illumination did not differenti-
ally affect display legibility. 
The effects of (1) three pointer-background contrast 
values, (2) two sizes of pointer end widths, and (3) 
three levels of ambient illumination upon the legi-
bility of EL displays were investigated. Both reading 
time and error results indicate that a wide pointer 
was significantly more legible under all conditions 
than the narrow pointer. Similar time and error results 
were found for the three contrast values, and the 50% 
contrast value, i.e., 2:1, being the most legible. 
Notes: 
1. The results of this investigation indicate that 
human factor criteria established on non-EL dis-
plays may not apply to EL displays. 
2. Inquiries concerning this innovation may be di-
rected to:
Technology Utilization Officer 
Manned Spacecraft Center 
Houston, Texas 77058 
Reference: B66-10316 
Patent status: 
No patent action is contemplated by NASA. 
Source: G. E. Miller and M. V. McLean 
of North American Aviation, Inc. 
under contract to 
Manned Spacecraft Center 
(MSC-494, 496, 501, and 505) 
Category 02 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19660000315 2020-03-11T17:39:11+00:00Z


Legibility of electroluminescent instrument panels investigated

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