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Flux sunset logo.svg
Developer(s) Michael Herf, Lorna Herf
Initial release February 2009; 5 years ago (2009-02)
Stable release Windows: v3.10
Mac OS X: build 30[1]
Linux: --
iOS: 0.985[2]
Development status Active
Operating system Microsoft Windows, Linux, Mac OS X, iOS
Available in English
License Proprietary, with free download. (with patent claim)
Website stereopsis.com/flux/

f.lux is a computer program developed by Michael and Lorna Herf. It adjusts a computer display's color temperature according to its location and time of day, based on a user specified set of longitude and latitude geographical coordinates, a ZIP Code, or a city name.

The program was designed to reduce eye strain during nighttime use and to prevent disruption of normal sleep patterns.


f.lux is available on all major operating systems, including Microsoft Windows, OS X, and Linux.

f.lux also is available on the iPhone, iPad, and iPod Touch, although it requires the device to be jailbroken. The developers also are working on a version for the Android operating system.[3]


f.lux is based on the hypothesis that adjusting the color temperature of the display to match the current time of day will not inhibit the secretion of melatonin during nighttime that is involved in Circadian rhythms. When nighttime arrives, f.lux automatically adjusts the color temperature (making whites appear reddish or salmon), thus reducing the display's brightness. While the f.lux program has yet to be scientifically tested, studies in circadian rhythms are pointing to effects of color temperature on melatonin secretion. For example, in a study by Morita et al, color temperature differences dropping from 6500K to 3000K at 1000 lumens resulted in a differential increase in melatonin level production from about 300 pg/hour (higher color temperature; more blue light) to 600 pg/hour (lower color temperature; more red light). Control subjects excreted 1000 pg/hour under 50 lux intensity.[4]


f.lux automatically calibrates the computer or device display's color temperature to the time of the day. The user also has the option of choosing a color preset or disabling f.lux for an hour and returning the screen to its normal calibration. The software offers five preset color settings on OS X: candle, tungsten, halogen, fluorescent, and daylight.[3] For Microsoft Windows, the halogen, fluorescent, and daylight settings are available—as well as Incandescent on beta. The iOS version uses the same presets as the Mac version.

A "Movie Mode" is available on Windows and OS X that reduces the adjustment for 2.5 hours, which is long enough for viewing most feature films.

The software requires the device's location in order to determine its local sunrise and sunset. Currently the program does not work for locations that are above 65° North.

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