Dark mode is a user interfaces (UI) for content that displays light text on a dark background. Dark mode is especially helpful for those viewing mobile computing device screens at night. The reduced brightness can reduce eye strain in low light conditions. Dark mode can also be used as a courtesy in situations when a screen's bright light might annoy others.
Interest in dark mode has increased along with public awareness in how ambient light affects circadian rhythm and sleep/wake cycles. Many popular websites and online services currently offer dark mode, including YouTube, Facebook Messenger, Windows 10. Often Dark mode is a hidden option. In messenger for iOS, for example, dark mode is enabled by sending a moon emoji and tapping it to show the hidden option. In Windows 10 it is enabled by way of a command entered into PowerShell:
“New-ItemProperty -Path HKCU:\SOFTWARE\Microsoft\Windows\CurrentVersion\Themes\Personalize -Name AppsUseLightTheme -Value 0”