F.lux

Functionality

On installation, the user can choose a location based on geographic coordinates, a ZIP code, or the name of a location. The program then automatically calibrates the device display's color temperature to account for time of day, based on sunrise and sunset at the chosen location. At sunset, it will gradually change the color temperature to a warmer color and restore the original color at sunrise.

f.lux offers a variety of color profiles and pre-defined temperature values, modifying program behaviour for specific programs or activities; including a mode for film watching, decreasing red tinge (for 2.5 hours), and a darkroom mode that does not affect night-adapted vision. Times can be inverted on f.lux for PC to provide warm lighting during the daytime (for people who work at night). The program can control Philips Hue LED lighting, so that the color temperature of house lights follows f.lux's settings.

Platforms

The program is available for Microsoft Windows, macOS and Linux (except for Ubuntu 18.04 LTS). It is also available for Apple iOS devices, although it requires the device to be jailbroken. Apple has not allowed the application in its App Store due to its use of restricted developer tools. The developer briefly hosted an Xcode project on GitHub, allowing iOS 9 users to sideload the application onto their devices, but retracted it at the request of Apple. Following Apple's announcement of a similar function, called Night Shift, in iOS 9.3, the developer called upon Apple to provide developer tools and to allow their application into the App Store. A preview version for Google's Android system is available.

Efficacy

Reducing exposure to bright (1000 lux) blue lights at night time was linked to increased melatonin secretion in a 1996 study but a 2018 study showed that changing the spectral composition of self-luminous displays without changing their brightness settings may be insufficient for preventing impacts on melatonin suppression.

f.lux proponents hypothesize that altering the color temperature of a display to reduce the prominence of white–blue light at night will improve the effectiveness of sleep. Although the developer provides a list of relevant research on their website, the program itself has not been scientifically tested to determine its efficacy, and the equivalent Apple program, Night Shift, was shown to have no effect on sleep outcomes (sleep latency, duration, efficiency and wake after sleep onset) in a 2021 study on 167 college undergraduates. f.lux has been widely and positively reviewed by technology journalists, bloggers, and users.

References

References

1. "f.lux for iOS". f.lux.
2. (October 31, 2013). "Review: f.lux makes your computer usable at night".
3. (October 15, 2014). "Save Your Eyes and Improve Your Sleep with f.lux for OS X and Windows".
4. "f.lux: F.A.Q. - I work nights. How do I flip the day and night settings?".
5. "f.lux has been updated to a new version".
6. (October 23, 2014). "Reduce Eye Strain and Get Better Sleep by Using f.lux on Your Computer".
7. Hern, Alex. (January 12, 2016). "Apple promises a good night's sleep with new iPhone feature". [[The Guardian]].
8. Tepper, Fitz. (November 12, 2015). "F.uxd: Apple Says Screen Brightness App Violates Developer Agreement".
9. Perez, Sarah. (January 15, 2016). "F.lux Asks Apple To Let Its Screen Color Adjustment App Back Into App Store".
10. "f.lux Home Page".
11. (1996). "Effects of Lights of Different Colour Temperature on the Nocturnal Changes in Core Temperature and Melatonin in Humans". Journal of Physiological Anthropology.
12. (May 2019). "Does the iPad Night Shift mode reduce melatonin suppression?". [[Lighting Research & Technology]].
13. (August 2021). "Does iPhone night shift mitigate negative effects of smartphone use on sleep outcomes in emerging adults?". Sleep Health.