Automatically Change Screen Color To Reduce Eye Strain

F.lux is a free utility to automatically change your screen color temperature according to the time of day – warm at night and like sunlight during the day. It is available for Windows, Mac, Linux and iPhone/iPad/iPod Touch (must be jail-broken).

Why Use F.lux? The color temperature of a computer screen is not the same as brightness or contrast – cool colors are blueish white (like sunlight) whilst warmer colors are yellowish white. Computer screens are typically set to use cool colors (the same color temperature as sunlight) – all the time.

This is fine during the day but it can tire your eyes at night – humans aren’t designed to be looking at sunlight after sunset. Research suggests that night-time exposure to blue light keeps people up late – after using it for a few days, it does seem to help reduce eye strain – and may help you sleep too.

Main Features

  • F.lux uses the co-ordinates of your current location to calculate the times of sunset and sunrise so it can automatically change the color temperature for you.
  • When the sun sets, it makes your screen look like your indoor lights. In the morning, it makes your screen look like sunlight again.
  • You can disable the program for an hour at a time if you are doing color-sensitive work e.g. image editing.
  • You can change the transition speed of the switch between day and night colors – choose between 20 seconds or a more gradual change over the course of an hour.
  • You can change the color of the night (and day) lighting to suit your home/preferences.

Using F.lux – Download and install it from the official website here (it was written by Michael Herf, a programmer of Picasa) – the following comments are for Windows users but the principles are similar for all versions. Run the program and press the ‘Change Settings’ button to open the Settings:


Click the ‘Change’ button to Set your Location – this opens the ‘Where Am I’ window where you need to enter your longitude and latitude so that F.lux can calculate your sunrise and sunset:


The simplest way to find these co-ordinates is to visit the Maps page here and enter your town/city – it uses Google Maps to display your longitude and latitude co-ordinates:


Copy and paste these co-ordinates into the ‘Where Am I’ window then press OK to finish. You have now set up the program to run with its default settings.

F.lux Options – Right click the F.lux icon in the taskbar to display settings where you can change a variety of options:

F.lux Settings

‘Change Lighting’ lets you edit the default light settings – press and hold the night button (orb) and slide it across the scale to match your night lighting. Press ‘Done’ when you have finished and wait for night-time for F.lux to swing into action.

By default the program is set to check for updates daily – this seems overkill so you may wish to disable the check.

It is set to run automatically when you start Windows which makes sense (and it only uses about 3MB of RAM) – there is no menu option to disable it. If you really wanted to disable it from startup, untick the F.lux entry in the Startup tab of Msconfig (see how to use Msconfig) – remember that you would have to run the program manually every time you start up…


You could say that F.lux is a warm, not cool program ;-)

The night-time color takes a bit of getting used to but after a few minutes your eyes adjust and you get accustomed to the warmer color temperature – it can make using a computer screen at night a less glaring and tiring experience.