Summary: In people with normal vision (or corrected-to-normal vision), visual performance tends to be better with light mode, whereas some people with cataract and related disorders may perform better with dark mode. On the flip side, long-term reading in light mode may be associated with myopia.
Introduction
Recently, spurred by the introduction of dark mode in IOS 13, a reporter asked me to comment on the usability of dark mode and its popularity as a design trend. It’s a question that I also got several times from attendees to our UX Conference.
I must say upfront that NN/g has not done its own research on dark mode. However, these questions prompted me to do a review of the academic literature on whether dark mode has any benefits for users — with normal vision or not. I will share these findings with you.
But first, let’s make sure we’re all on the same page by defining some vocabulary.
Definition: Contrast polarity is a term used to describe the contrast between the text and the background: Positive contrast polarity (light mode) refers to dark-font text on light background.
refers to dark-font text on light background. Negative contrast polarity (dark mode) denotes the combination of light (e.g., white) text on dark (e.g., black) background.
Dark-mode displays emit less light than light-mode ones (and, because of that, they might extend battery life). But the amount of light in the environment influences not only power consumption, but also our perception. In order to understand how, let’s briefly review some basic information about the eye pupil and how it reacts to the amount of light in the environment.
The Human Pupil Is Sensitive to the Amount of Light
The human pupil is the gateway to the retina: through it, light reaches the eye. By default, the human pupil changes size depending on the amount of light in the environment: when there is a lot of light, it contracts and becomes narrower, and when it’s dark, it dilates to allow more light to get in. Smaller pupil sizes make the eyes less susceptible to spherical aberrations (in which the image appears unfocused) and increase the depth of field, so people don’t have to work so hard to focus on the text, which, in turn, means that their eyes are less likely to get tired. (Camera apertures work exactly in the same way: a photo taken at f/2.8 will have a narrower depth of field and thus more blurring than one taken at f/16.)
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