F.lux: Tom's Mac Software Pick

Keep the Blues at Bay for Better Sleep and Less Eye Fatigue

F.lux: Tom's Mac Software Pick
Screen shot courtesy of Coyote Moon, Inc.

Long before Apple added Night Shift to iOS 9.3, F.lux was performing the same color temperature management magic on Macs and iOS devices, as well as Windows, Linux, and Android systems. F.lux has been around for a while, championing the idea that a display's color balance shouldn't be stagnant, but should change over time, just as the day’s light changes from warmer colors during sunrise, to daylight blues at noon, and back to warm colors at sunset.

During the nighttime hours, F.lux reduces the blue spectrum in a display, producing an image that better matches natural lighting colors, and reducing eyestrain.


  • Automatic display adjustments based on location, time of day, and type of lighting present in the room.
  • Users can adjust color temperature settings to meet their needs.
  • Special settings for sleeping in on weekends.
  • Darkroom mode to preserve night vision.
  • Movie mode preserves color and shadow details for watching videos.
  • Able to switch themes between daytime and nighttime.


  • Display flicker reported for some users (can be eliminated with preference settings).

The basic concept of F.lux is simple enough: adjust the color balance of your display to match your surroundings. The main benefit would seem to be a reduction in eyestrain, something many of us who spend a good deal of time at our Macs could use.

However, the developer also points to research that suggests being bombarded by the daylight color spectrum for long periods of time can also affect our sleep patterns, causing loss of sleep and difficulty getting to sleep, as well as problems staying asleep.

The evil component in the light spectrum seems to be blue light, which is in abundance during natural daylight, and lacking when nighttime falls. If you work with your Mac into the night, your brain may be getting some mixed signals; the display, which is giving off a daylight spectrum, may be telling your brain that the sun is still up, while the clock is telling you that you should have been in bed an hour ago.

F.lux can fix the display spectrum issue by adjusting the color balance to mimic how nature intended the lighting spectrum to change from day to night.

Setting Up F.lux

Installing F.lux is as simple as dragging the downloaded app to your/Applications folder, and then launching the app. On first launch, F.lux opens to its preference settings. The first thing you should do is configure the location information, so the app can coordinate the proper timing for daytime, sunset, night, and sunrise.

Once the location is set, you can adjust the color balance to meet your needs. You can use F.lux’s built-in presets: Recommended colors, Classic F.lux, Working Late, or Custom colors. You can use any of the presets as a starting point, then customize as you wish, although I highly recommend starting with the Recommended colors or Classic F.lux presets, and giving them a try for a few days.

If you decide to customize the color balance settings, F.lux allows you to change the color temperature for Daylight, Sunset (the same color temperature will be used for sunrise), and Bedtime. To adjust the color temperature, just select the time (Daylight, Sunset, or Bedtime), and then drag the color temperature slider from normal (daylight hours) to the warm colors. Along the way, the slider will display the color temperature, as well as highlight the color temperature for various lighting sources, such as Tungsten (2700K), Halogen (3400K), Fluorescent (4200K), Sunlight (5500K), and Daylight (6500K).

While I recommend using the default settings to start with, you may want to adjust the daylight setting to match the type of lighting you use with your Mac. My Mac is located in a room with a larger window and skylights. There's little, if any, indoor lighting in use during the daytime, so I set the daytime color temperature to 6500K, the normal daylight setting. On the other hand, if you're in an office full of fluorescent lighting, you may want to try matching that color temperature for your daylight setting.

Once you have the color temperature and location set, you can click the Done button.

Using F.lux

Once you finish the setup, the F.lux preference window disappears and the app appears only as a menu bar icon. F.lux can pretty much take care of itself from here, automatically adjusting the display color as needed. But for those of us who love to fiddle, F.lux has a few options available from its menu bar icon.

First up, Fast Transitions. Normally, F.lux takes its time changing from daylight to sunset to nighttime. You can speed up the process by selecting fast transitions, just the thing for those of us who think a sunset takes too long, or who just want to see F.lux do its stuff quickly at the transition points.

Sleep in on Weekends mode delays the transition to daylight on weekends.

Extra Hour of Sleep: yeah, that’s the option I want; once again, it will delay the transition to daylight.

Under Color Effects, you'll find Dark Room, which removes all blue light and green light from the display and inverts colors. The result is a dark display with red text. Could be very helpful for nighttime use when you need to preserve nighttime vision, say when working with a telescope.

Movie mode preserves color and shadow details for a 2.5-hour period.

OS X Dark Theme uses your normal Mac settings during the day, but at night switches to the optional dark theme, which changes the dock and menu bar to a black background.

You'll also find a disable option on the menu, very handy when you find yourself needing accurate color balance, say when working with images.

Final Thoughts

Although I didn’t encounter the issue, the developers at F.lux mention that those using OS X El Capitan may experience a flickering issue with Mac’s display. The problem seems to be an interaction between F.lux and the system preference to automatically adjust brightness. You can turn the display preference off by selecting System Preferences, Display, and then removing the checkmark from the Automatically Adjust Brightness checkbox.

Aside from this one con, which I actually didn’t run into, F.lux works very well, adjusting Mac’s color temperature to better mimic how nature changes lighting conditions. As to the effect on sleep, I’ll leave that to others to argue about. I just know that if I were having sleep issues, I would certainly add this app to my Mac; there's no harm in giving F.lux a try.

Even without sleep issues, F.lux allows you to gain better control over your display, adjusting color temperature to match your background lighting conditions, as well as easily disabling F.lux when the need arises.

F.lux is free; donations are accepted.

See other software choices from Tom's Mac Software Picks.