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http://hdl.handle.net/1947/9859
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| Title: | Identification of Text and Symbols on a Liquid Crystal Display Part II: Contrast and Luminance Settings to Optimise Legibility. |
| Report number: | DSTO-TR-2144 |
| AR number: | AR-013-965 |
| Classification: | Unclassified |
| Report type: | Technical Report |
| Authors: | Fletcher, K.
Sutherland, S.
Nugent, K. |
| Issue Date: | 2009-02 |
| Division: | Maritime Operations Division |
| Abbreviation: | MOD |
| Release authority: | Chief, Maritime Operations Division |
| Task sponsor: | COMAUSNAVSURFGRP |
| Task number: | NAV 07/094 |
| File number: | 2008/1038913 |
| Pages or format: | 17 |
| References: | 32 |
| DSTORL/DEFTEST terms: | Liquid crystal displays
Visual acuity
Data visualisation
Image identification
Human fatctors engineering |
| Other descriptors: | Naval displays |
| Abstract: | This study aimed to identify the luminance and contrast levels necessary to minimise the threshold identification size of bright letters displayed over a dark background on an LCD under low (1.5 lux) and high (260 lux) lighting conditions. White, pure red, pure green and pure blue upper-case Bailey Lovie letters with a contrast between 3:1 and 300:1 were displayed on an LCD to 20 participants. The threshold identification size was equivalent for all colours except for blue, which had larger threshold identification size than white, red and green at all character luminance levels tested. The threshold identification size initially decreased as character luminance increased, but asymptoted to a minimum size after which further increases in character luminance yielded no additional significant reduction in the threshold identification size. The threshold identification size was relatively insensitive to contrast provided the contrast level was above 6:1. Self-report preferred character luminance levels were generally higher than the character luminance levels necessary to achieve minimum threshold identification size. It is recommended that character luminance should be approximately 20 cd/m2 under dark lighting conditions and approximately 60 cd/m2 under bright lighting conditions. These values translate to contrast levels of 20:1 and 60:1 under the suggested screen background luminance of 1.0 cd/m2. |
| Executive summary: | The Royal Australian Navy (RAN) ANZAC Class Frigates will be upgraded with an enhanced Anti-Ship Missile Defence (ASMD) capability. The upgrade involves the development of a new Combat Management System (CMS) that will use liquid crystal displays (LCDs). The legibility of text and symbols displayed on an LCD will be dependent upon their contrast and luminance, and may also depend on colour. If the contrast and luminance levels are poorly adjusted, text and symbol sizes may need to be larger than if optimal settings are used. This study aimed to identify the contrast and screen luminance settings that minimise the threshold identification size for white, primary red, primary green and primary blue letters displayed on an LCD similar to that planned for use in the ASMD CMS when viewed under the ambient light levels experienced in ANZAC operations rooms. The results should be directly applicable to the ASMD upgrade project as well as to LCDs generally.
The twenty DSTO volunteers who participated in the study attempted to identify white, pure red, pure green and pure blue letters presented on the LCD with contrast levels ranging between 3:1 and 300:1. Participants viewed the letters under low and high ambient lighting conditions comparable to the levels experienced in ANZAC ops rooms. Two screen-background luminance levels were used in the dark lighting condition: 0.2 cd/m2, which was the minimum uniform luminance that can be achieved at the minimum LCD backlight brightness setting, and 1.0 cd/m2, which is the minimum uniform luminance that can be achieved at the maximum backlight brightness setting.
Threshold identification size was equivalent for white, primary red and primary green characters at all contrast levels, but primary blue had a larger threshold identification size than the other colours. In addition, the LCD could not produce pure blue at high character luminance levels, thus it is recommended that pure blue not be used in the ASMD CMS. Cyan (an equal combination of blue and green) may be an acceptable alternative, as proposed by MIL-STD-2525B. The threshold identification size initially decreased as contrast increased, but asymptoted to a minimum level after which further increases in contrast yielded no additional significant reduction in threshold identification size. The threshold identification size was relatively insensitive to contrast, provided the contrast level was above 6:1. It is therefore suggested that contrast levels should be greater than 6:1. Self-report preferred character luminance levels were generally higher than the character luminance levels necessary to achieve minimum threshold identification size and it is recommended that text luminance be approximatley 20 cd/m2 under dark lighting conditions and approximately 60 cd/m2 under bright lighting conditions. This translates into contrast levels of 20:1 and 60:1 respectively under the suggested screen background luminance of 1.0 cd/m2. |
| Appears in Collections: | DSTO Formal Reports
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