F.lux

F.lux works by shifting the display's color temperature from a cool, blue-rich spectrum during the day to a warmer, amber-toned spectrum at night, based on the user's location and time of day. The software uses the user's latitude and longitude to calculate sunrise and sunset times, gradually transitioning the color temperature over a period of about an hour. Users can adjust the target color temperatures for day and night, with typical settings ranging from 6500K (daylight) to 3400K (night). The underlying principle is that exposure to blue light in the evening suppresses melatonin production, which can disrupt circadian rhythms and sleep quality. F.lux also offers a 'darkroom' mode that reduces the display to a very dim red light, intended for use in complete darkness.

F.lux is available for Windows, macOS, and Linux, with versions for iOS and Android requiring jailbreak or root access. The iOS version was removed from the App Store in 2016 after Apple introduced its own Night Shift feature, which offers similar functionality. On Android, F.lux requires root access to adjust the display's color temperature, but a non-root version using a screen overlay is available for devices with certain hardware. The software is free for personal use, with a paid version for commercial use. F.lux also integrates with hardware like the Philips Hue smart lighting system, allowing it to adjust room lighting in sync with the display.

The scientific rationale behind F.lux is supported by research on the effects of blue light on circadian rhythms. Studies have shown that exposure to blue light in the evening can delay melatonin onset and reduce sleep quality. However, a 2019 randomized controlled trial published in Sleep Health found no significant difference in sleep outcomes between participants using F.lux and those using a placebo app, suggesting that the real-world benefits may be modest. Despite this, F.lux has been widely praised by users for reducing eye strain and improving sleep, and it has influenced the development of similar features in major operating systems, such as Apple's Night Shift and Microsoft's Night Light.

F.lux was created by Michael Herf, a former Google engineer, and his wife Lorna, who also developed the popular image viewer Picasa. The software's name is a play on the unit of luminous flux, reflecting its focus on light. F.lux has a built-in 'disco' mode that cycles through colors, and it can be temporarily disabled for color-critical work, such as photo editing. The software also includes a 'sunrise alarm' feature that gradually brightens the display in the morning. F.lux has been used in scientific research as a tool to control light exposure in studies of circadian rhythms. In 2020, the developers released a version for the Raspberry Pi, expanding its use in DIY projects.

Color temperature

A measure of the hue of a light source, expressed in Kelvin (K), with lower values indicating warmer, more amber light and higher values indicating cooler, bluer light.

Circadian rhythm

The natural, internal process that regulates the sleep-wake cycle and repeats roughly every 24 hours.

Melatonin

A hormone produced by the pineal gland that regulates sleep, with secretion increasing in darkness and suppressed by blue light.