Dark themes, often referred to as dark mode or night mode, are increasingly popular for user interfaces in digital devices and involve displaying light-colored text and elements on a dark background. The science behind the effectiveness and preference for dark themes involves a mixture of visual ergonomics, energy efficiency, and user comfort.
Visual Ergonomics and Eye Strain:
Dark themes can reduce eye strain by minimizing screen glare, especially in low-light environments. When the surrounding light levels are low, a bright screen can cause discomfort and lead to increased eye fatigue. Since dark themes emit less blue light compared to bright themes, there is a reduction in the negative impact that prolonged exposure to blue light can have on sleep patterns and eye health.
Readability and Contrast:
While dark themes can be easier on the eyes, especially in dark environments, there are trade-offs in readability. High contrast between text and background is essential. Poorly designed dark themes can result in reduced legibility if contrast levels are too low. For screens with high brightness and resolution, a well-defined contrast ratio (typically white or light grey text on black background) can enhance readability without causing significant eye strain.
Battery Efficiency:
On OLED and AMOLED screens used in many modern smartphones and displays, dark themes can save battery life. This is because these screens produce colors by turning on individual pixels, and black pixels are ‘off’ pixels consuming practically no power. Consequently, interfaces that use dark modes effectively contribute to longer battery life in such devices.
User Preferences and Aesthetics:
Many users find dark themes aesthetically pleasing and modern. Preferences can be subjective, but the availability of dark mode offers users additional customization based on personal comfort and taste, enhancing user experience by allowing adaptation to various lighting conditions.
Circadian Rhythms:
Exposure to bright white and blue light before bedtime can interfere with circadian rhythms by suppressing melatonin production, the hormone responsible for sleep regulation. Dark themes, by reducing blue light emission, may help in minimizing this effect, potentially aiding better sleep patterns when used during nighttime.

While dark themes have their advantages, they might not be suitable for everyone or all use cases. Ultimately, the effectiveness of dark themes comes down to individual user preferences, the specific environment in which they are used, and how well they are implemented in terms of contrast and accessibility.