Apple, which has already introduced "dark mode" in macOS, is widely expected to replicate this in its mobile operating system iOS this year. The move comes as a number of technology companies introduce dark mode in their apps and operating systems. But is it something everyone wants?
TidBITS: When text is white on a black background as it would be in Dark Mode, the whiteness of the lines lightens the edges of each line broadly on both sides, blurring the edge. If the thin lines of the text are black and the background is white, however, white from both sides washes over the entire line, lightening it evenly, so the edges aren't blurred. Blur is a bad thing because of how the human eye relies primarily on contrast when extracting detail from an image. In "Reality and Digital Pictures" (12 December 2005), Charles wrote: The eye does not see light per se, it sees changes in light -- contrast. If two objects do not contrast with one another, to the eye they meld into one. This fact makes controlling the contrast of adjacent details to be paramount in importance. He was focused on issues revolving around photographs, but contrast has been shown to be paramount in numerous studies of textual legibility as well.
Of course, contrast goes in both directions -- black on white and white on black both have high contrast. In the scientific literature, black on white is called "positive polarity," whereas white on black is called "negative polarity." Numerous studies over decades of research have found that positive polarity displays provide improved performance in a variety of areas. [...] Taptagaporn and Saito (1990, 1993) tracked changes in pupil size for different illumination levels as well as for the viewing of different visual targets, such as a cathode ray tube (CRT) display, script and keyboard. They found less visual fatigue as measured by the frequency of changes in pupil size when working was accomplished with a positive than with a negative polarity display. Likewise, Saito, Taptagaporn, and Salvendy (1993) found faster lens accommodation and thus faster focusing of the eye with positive than with negative polarity displays.
To summarize, a dark-on-light display like a Mac in Light Mode provides better performance in focusing of the eye, identifying letters, transcribing letters, text comprehension, reading speed, and proofreading performance, and it results in less visual fatigue and increased visual comfort. The benefits apply to both the young and the old, as that paper concludes: In an ageing society, age-related vision changes need to be considered when designing digital displays. Visual acuity testing and a proofreading task revealed a positive polarity advantage for younger and older adults. Dark characters on light background lead to better legibility and are strongly recommended independent of observer's age.
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