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Yu-Chi Tai, Shun-nan Yang, Kevin Larson, James Sheedy; Interaction of Ambient Lighting and LCD Display Polarity on Text Processing and Viewing Comfort. Journal of Vision 2013;13(9):1157. doi: 10.1167/13.9.1157.
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© ARVO (1962-2015); The Authors (2016-present)
Liquid crystal displays (LCDs) present text by differentially twisting LCs to adjust the amount of backlight emitted to illuminate the characters. While LCDs provide ample luminance and contrast in most conditions, text quality deteriorates along with slower reading and increased viewing discomfort under dim lighting. The current study compared viewing comfort and performance under dim-to-normal lighting with different display polarity and size of visual field.
56 adults performed Threshold-Sized-Single-Letter Identification (TSSLI) and Normal-Sized-Word-Spelling-Check (NSWSC) tasks for 3 minutes each with 3 display polarity (positive/black-on-white, negative/white-on-black, black-on-grey), 2 (big, small) visual field and 5 lighting conditions (20, 44, 99, 220, 480 lux). Accuracy, speed, viewing distance, and viewing comfort were compared.
Opposite performance pattern was observed between TSSLI and NSWSC. Accuracy and speed were better with positive polarity for TSSLI but better with negative polarity for NSWSC. Viewing distance was shorter with smaller visual-field and negative polarity, especially with TSSLI. With TSSLI, subjects reported blurry text and poor text contrast with negative polarity, but stronger glare with positive polarity in large visual-field, but no significant discomfort with NSWSC.
The results suggest a significant interaction among ambient luminance, pupil size, and viewing discomfort. With TSSLI on positive polarity (a single small back letter on a huge white space), the bright background likely caused pupillary constriction, reduced peripheral optical aberration, and resulted in clearer retinal image for better identification (pinhole effect) but also induced stronger sense of glare. In contrast, negative polarity enlarged the pupil and caused blurry text. The vast dark background likely manifested specular reflection and reduced letter clarity. With NSWSC, however, text form was clearly visible regardless of display polarity but dark background was less stimulating and more comfortable for viewing. Overall, subjects preferred display that is less stimulating to the eyes (i.e., negative polarity and black text on gray).
Meeting abstract presented at VSS 2013
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