Light Mode vs. Dark Mode: Energy & Creativity vs Focus & Productivity? (And oh yes, eye strain)

Overview

• Positive contrast polarity (light mode) 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.

Early studies conducted in the 1980s seemed to point out that, for people with normal vision or corrected-to-normal vision (i.e., wearing appropriately prescribed glasses or contacts), the contrast polarity did not affect visual performance.

However, some more recent studies contradict those earlier findings.

One-time / Brief Use

one, published in 2013 in the journal Ergonomics, looked at visual acuity and reading performance, and the other one, published in 2017 in Applied Ergonomics, investigated performance for a glanceable-reading task — the quick reading of 1–2 words that people often engage in when they interact with a mobile phone, a smartwatch, or a car dashboard and that is involved in activities such as checking directions or attending to a notification.  

The first study showed that light mode won across all dimensions: irrespective of age, the positive contrast polarity was better for both visual-acuity tasks and for proofreading tasks. However, the difference between light mode and dark mode in the visual-acuity task was smaller for older adults than for younger adults — meaning that, although light mode was better for older adults, too, they did not benefit from it as much as younger adults, at least in the visual-acuity task.

When researchers looked at fatigue metrics, they concluded that there was no significant difference of contrast polarity on any of them (meaning that it wasn’t the case that dark mode made people more tired, or vice versa).

Another study, published in the journal Human Factors by the same research group, looked at how text size interacts with contrast polarity in a proofreading task. It found that the positive-polarity advantage increased linearly as the font size was decreased: namely, the smaller the font, the better it is for users to see the text in light mode.  Interestingly, even though their performance was better in the light mode, participants in the study did not report any difference in their perception of text readability (e.g., their ability to focus on text) in light versus dark mode — which only reinforces the first rule of usability: don’t listen to users.

The study found that lighting, polarity, and text size all had an effect on performance — in the direction perhaps expected by now: simulated daytime led to faster judgements than simulated nighttime, light mode was better than dark mode, and bigger font was faster than smaller font. The interesting result was the significant interaction between ambient lighting and contrast polarity: during daytime, there was no significant effect of contrast polarity, but during nighttime, light mode led to better performance than dark mode. Moreover, during nighttime it was much harder for people to read small-font text in dark mode than in light mode.

The lack of effect of polarity in simulated daytime environments was somewhat surprising and inconsistent with a different older study by Buchner and Baumgartner, that also looked at bright vs dark ambient conditions. However, in that study the bright ambient light was much lower than the one used in the Agelab study (think office light versus bright outdoors light). Dobres and his colleagues argue that the amount of ambient light may affect the positive-polarity advantage, with bright light leading to zero difference, but normal office light still being able to produce a difference.

Long-Term Use

References

https://www.nngroup.com/articles/dark-mode/