F.lux 4 beta Review (Windows)

The popular software for blue light reduction f.lux alternative to Iris has new major version with lots of new features and improvements. The new version is v4 and it’s a major improvement over the several year old version v3.

The goal of this post is to review all this new and exciting features.

You can download the f.lux beta version from the official website.

If for some reason you can’t find the it use this button

[Download not found]

After the download is complete the installation is pretty straight forward. Start the .exe file then

If this is the first time you install f.lux you will be prompted to unclock the device gamma. This is done so f.lux can set color temperature lower than 3400K

It’s ok here to click Yes. F.lux will write to the registry this key

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\ICM]

Which is the way to unlock the gamma under Windows. If for some reason after this you have problems with the colors of your screen or inverted colors or broken screen somehow then delete this key and restart your system.

The installation is now finished and f.lux is installed into the Local folder of your PC

From here you can click uninstall.exe if you for some reason cannot find the Uninstaller.

After this you will get this notification which will prompt you to Restart your PC.

This is to unlock the low Color temperature values. Let’s for now ignore it and click Later.

You will also be prompted to enter your Location

f.lux will use your location to calculate the sunset and sunrise times. f.lux uses this data to gradually change it’s settings when the night is comming and when the day is comming.

Enter your location, click Search, then click Ok.

You are now all set up and this is how f.lux 4 beta looks like

One thing I noticed is that when not on focus this window will automatically close itself which is kind of annoying at least for me when writing this review. It takes something like 5 seconds to auto close itself.

Aside from this I do think that the closing transition is really nice and as a programmer I know that they have spend a lot of time perfecting it. It’s really stylish.

You will also have Thank you for installing f.lux page loaded in your browser

From here you can read about some tips, changelog and money to the f.lux software LLC.

The f.lux team is asking for 5$ which I personally think is small amount for the amount of work they have done, but maybe after the sale of Picasa they are just wealthy enought not to care about money.

I tried several times the donation model for Iris and made exactly 0$ after a year of free software, but I hope this is working for them.

They also have a survey with the following questions

– We want to know about your screen. Do you have a tape measure handy? (If not, you can guess.)
– How big is the screen you usually use for bed (the “diagonal”, in inches)? – If you have two screens, just answer the biggest one.
– And, how many inches is it from your eyes?
– Does your screen usually dim itself when the light changes?
– Do you dim the rest of the lights in your room?
– How old are you (years)?
– Do you usually go to bed at the same time every night?
– When do you wake up, if you can sleep in?

At first glance this tells us that their plan is to match the indoor lighting to the time of the day and this is actually the description of their company:

f.lux makes software to help you see the right kind of light at the right time of day. f.lux automatically warms up your computer’s screen colors at sunset and returns them to normal at sunrise.

f.lux will automatically start when your computer starts and it will run to the left of your system clock.

One thing I don’t like is that this icon automatically shows itself when f.lux is started and there is no way to hide it. Even if you hide it the next time you start f.lux it will pop up again

And the next start

Maybe this is user friendly for non-technical people, but I find it annoying. About the new things.

Update: In version 4.29 this tray icon now stays hidden if you hide it.

f.lux version 4

What’s new:

  • Analyzes your displays to show you how bright they are to your body: adjust your backlight and watch!
  • Bedtime mode: warmer light before bed gets you ready for sleep, and works with all kinds of schedules
  • Disable by app (so you don’t forget Photoshop)
  • Backwards alarm clock: reminder not to stay up late
  • Presets to help adjust your settings
  • Color filters for eyestrain and other uses
  • A wider range of color settings
  • New hotkeys to adjust color (alt+shift+PgUp and alt+shift+PgDn)


  • Reduced impact on game framerates
  • Resolution independent interface, for high DPI displays
  • DisplayLink monitors (connected by USB) work in a lot more cases now

Smart Lighting:

  • Hue integration now supports more light types
  • LAN API with support for telling other devices when f.lux changes

f.lux version 3 (2013)

If you’ve used f.lux before, this version now has these changes:

  • Expanded color temperature settings, down to 2700K, and some presets lower than that, down to 1200K.
  • Display warms up as your backlight dims (works with laptops)
  • Movie mode
  • Disable until sunrise
  • A simple control for Philips Hue lights
  • Hotkeys to dim your screen (Alt-PgUp, Alt-PgDn), so desktop users can dim too, and a hotkey to disable (Alt-End)

f.lux version 1 (2009)

This is just for the complete histrory. How the first version looked like and to see the progress 🙂

If you ask me the first version seems the best. Yes the UI looks more ugly, but it’s so simple and easy to understand. Also I’m not sure how many users want a program to tell them when to sleep. People just want the orange screen.

f.lux explanation

Computer screens, tablets and mobile phones emit full spectrum light around the clock, just like the sun. Exposure to blue light at the wrong time of day can keep you awake later and interfere with the quality of your sleep. f.lux tries to help this by removing blue and green light to help you wind down in the evenings.

It can take a few days to get used to the new colors at night, so we recommend setting the night-time colors in f.lux to whatever feels good to your eyes. After a few days with f.lux, experiment with the settings to warm things up a little more and find which color works best for you. Our default setting of 3400K on Windows removes about 3/4 of the blue and about half of the green light. You can remove even more alerting light by choosing “Expand color range” to unlock deeper colors in Windows (in the “Lighting at night” menu).

Enough with the introduction now let’s start with the explanation of the actual new beta version. Even without a restart f.lux can change the colors down to 800K, but it will it’s recommended to Restart your PC after first install so let’s now Restart our PC to unlock full color changes.

If you have missed to unlock gamma you can do this by hand by starting this file.

[Download not found]

And to lock the gamma

[Download not found]

After every lock or unlock you need to restart your PC for changes to take effect.

First thing now I want to highlight all the places which you can click to change some setting. I will then proceed to try to explain each setting in greater detail. The buttons inside red border are clickable.

Right click on the tray icon will also give some options to customize f.lux. Some things like the per app disabling are only available via the tray icon so this is important.

You can also click the close button from the main settings menu, but I guess I don’t need to tell you this and f.lux is going to automatically close itself if the window is inactivate for several seconds.

Leaving all things default, the most important thing you need to know about is the Color temperature slider.

Moving it during different times of the day will do different things. f.lux has 4 different modes:


Color temperature settings during the day.



The period when f.lux prepares your melatonin for your wake time.

Bedtime (Late)

The period when you are supposed to be sleeping.


The period when transition between modes happens.

I tried really hard, but I still don’t seem to understand the difference between Sunset and Bedtime mode. It actually seems kind of a bug, because when you set your wake time to 5:00 PM you have 2 days periods which is really strange.

Maybe there is some really complicated science behind this, but even I don’t seem to get it and I have read almost all medical researches and even created Iris which is similar blue light reduction software. I find this too complicated for users and I can’t find explanation anywhere on the internet.

I wrote my experiments with this in Trying to understand the f.lux schedule.

Now back to the Color temperature slider. Depending on which mode you are and which part of the day is the color temperature slider will change the current mode settings.

The range of the Color temperature slider of f.lux is from 1900K to 6500K by default. You can get bigger color range by clicking the settings menu

Then Options (and Smart Lighting)…

From here click Use wider slider ranges (1200K-9300K) and click Done

Now your Color temperature slider can go down to 1200K and up to 9300K

To get the smaller color range back uncheck Use wider slider ranges (1200K-9300K) from the same menu and click Done.

Now let’s look at the f.lux 4 beta presets. They are available in the right corner of the settings panel.

In the next several lines I will review every one of the current presets and what this means to you. Every preset have several important characteristics.

Name – Name of the preset. Example is Recommended colors

Description – Text explaining the preset. You can see the description of the preset in the title of the settings window. Example is Warm at sunset, with a candle before bed

Day – Color temperature during the day. Example is 6500K

Night – Color temperature during the night. Example is 3400K

Bedtime (Late) – Color temperature during bedtime. Example is 1900K (Candle)

Now I’m goind to review every of the current available presets.

Recommended Colors

Name – Recommended Colors
Description – Warm at sunset, with a candle before bed
Day – 6500K
Night – 3400K
Bedtime (Late) – 1900K

Working Late

Name – Working Late
Description – Bright after sunset, and wind down for bed
Day – 6500K
Night – 6500K
Bedtime (Late) – 2300K

Far from the Equator

Name – Far from the Equator
Description – A tinge of sunset, with a candle at bedtime
Day – 6500K
Night – 5500K
Bedtime (Late) – 1900K

Classic f.lux

Name – Classic f.lux
Description – Warm at sunset, and all night too
Day – 6500K
Night – 3400K
Bedtime (Late) – 3400K

Daytime Eyestrain

Name – Daytime Eyestrain
Description – Reduce eyestrain during the day, very warm at night
Day – 5500K
Night – 2900K
Bedtime (Late) – 1700K

Cave Painting

Name – Cave Painting
Description – Extra-warm light all the time
Day – 2700K
Night – 2300K
Bedtime (Late) – 1500K

Color Fidelity

Name – Color Fidelity
Description – Smaller adjustments, better for color accuracy
Day – 6500K
Night – 5000K
Bedtime (Late) – 3400K

Adding your own Presets

Now let’s get our hands dirty by hacking f.lux a little and adding our own custom presets. Presets are located in file named preset.json which looks like this

If we first close f.lux then add our own preset Orange with the following data

	"name": "Orange",
	"desc": "My orange screen preset",
	"day": 5000,
	"night": 3400,
	"late": 2400

Don’t forget to add before your custom preset this file will look like this

Now if we try to start f.lux it’s going to delete our new preset and replace it with the default. I guess they will fix this in the future or maybe not, but this is not going to stop us.

One way f.lux not to delete your own custom preset is to plug out your internet cable. It looks like f.lux is downloading this preset.json file from their server on every start and it overrides our own custom preset.

This will obviously not work, because we will now not have internet, but there is also other solution. If you are ok not to have access to the https://justgetflux.com/ we can black list this website in our hosts file.

I will show you the manual way, but I’m sure there is some program to automate this. Iris for example had this feature before, but I remoded it since it didn’t make sense for eye protection.

Maybe I will make new software with the sole goal to block websites. So the hosts file is located in the


folder. Here is screenshot from my explorer.

You need admin access to open this file so run Notepad as Administrator

Then open the hosts file and add the following line justgetflux.com

Note that now you will not have access to the justgetflux website

To get access to the website if you want to not use your own preset open this file again and remove the line you just added.

Now we can add our own custom presets to the preset.json file. This file is located in the


folder. From here open the file preset.json and add your own custom presets.

Here are some presets to get the idea.

The minumum possible value of f.lux color temperature is 800K and the maximum possible color temperature is 10000K.

Now let’s finally open the f.lux program and see our awesome new presets.

And here is what they do:


Name – Orange
Description – My orange screen preset
Day – 5000K
Night – 3400K
Bedtime (Late) – 2400K


Name – Biohacker
Description – Biohacker mode
Day – 800K
Night – 800K
Bedtime (Late) – 800K


Name – Coffee
Description – Sleep is for losers
Day – 100000K
Night – 100000K
Bedtime (Late) – 100000K

I think I spend too much time playing with the f.lux presets so let’s go to the

Live preview graph

When you left click the live preview graph you will see how f.lux will change your screen colors during the next 24 hours. This is usefull to test how the different presets work.

I made a video showing how all the different f.lux presets change your screen colors during the next 24 hours.

The live preview graph is really usefull to test how your computer will look like during the night if it’s day now and how your computer will look like during the day if it’s night.

It’s really uncomfortable experience to start the live preview during the night, because the screen turns really blue so be carefull. You were warned 🙂

Wake time

The one thing I know for sure for the wake time is that if your wake time is 7:30 AM the day mode of f.lux will start at 7:30 AM

Aside from this there seems to be some circadian clock into f.lux which depending on your wake time will change the day and night times of f.lux. Here is a video of me playing with the wake time.

I also wrote dedicated article on trying to decode the wake time here Trying to understand the f.lux schedule.


Your location is used by f.lux to calculate the sun position. Combine this with your system clock and f.lux can calculate if it’s sunrise or sunset and if it’s day or night.

This is really important, because the entire program is tied to this values and the goal is to make your sleep schedule. Clicking this box will open window from which you can change your location.

For example during the same system clock in Sofia, Bulgaria the graph looks like this.

And in New York City like this

If you don’t like the default settings for your location you need to play with the longitude and latitude of different cities around the world.


You can see the info box in 2 places. The first is in the center of the settings panel and the second is when you hover the tray icon.

During the day info box will show something like:

Sunset in 3 hours, Wake: 9 hours ago

During the night info box will show something like:

Sunset: about an hour ago, Wake in 11 hours
Sunset: 2 hours ago, Wake in 10 hours

During the bedtime info will also show something like:

Sunset: 5 hours ago, Wake in 7 hours

Backwards alarm clock

During bed time f.lux will remind you how much time until waking up are remaining

Starting about 9 hours before your wake time, and once every 30 minutes, the backwards alarm clock will calculate how much sleep you will get if you go to bed right now. You can disable it from the f.lux settings menu to the left of your system clock.

Settings button

The final element of the settings panel is the settings button which opens f.lux to much more customization that you can dream of

Before we dive into the f.lux settings button menu let’s first look at the info next to the settings button. During the day it will show that The sun is up

After sunset it will show that The sun has set

And during bedtime the text will be You’re getting sleepy

Now let’s look at the settings button menu

You can get almost the exact menu when you right click the tray icon

The only difference is that in the settings panel the first option will be Adjust all colors at once, while in the tray menu will be f.lux color and schedule… which will actually open the settings panel. Also in the tray menu you also have Change location.

Note that you can also open the settings panel by left clicking on the tray icon. Middle click seems to do nothing.

Now let’s review all the items in the f.lux settings menu.

Adjust all colors at once

Click Adjust all colors at once if you want to change the settings on each different period of the day. Moving slider 1 will control the day part of the day and this is the period when the sun is up.

If you move any of the sliders too much it will also cause other sliders to move too.

If at the moment it’s bedtime in Adjust all colors at once menu the bedtime slider will have bigger width of the dot than the other sliders

Sometimes this is behavior which you may want and sometimes it’s now. In order to not move other sliders along with the first you can hold the Ctrl key while moving the slider. This will not cause other sliders to move.

Holding Ctrl key is really usefull, because sometimes you want to fixate only 1 slider, but all others are moving. This is one trick to not be frustrated by this.

Sunset slider controls the color temperature after sunset. This is the time between day and bedtime.

Bedtime slider controls the color temperature after sunset and before sunrise. This is the time when you are supposed to be sleeping.

Depending on the time of the day the slider in the simple settings view correspond to the slider of this part of the day.


Here is a video how to play with this settings with and without holding the Ctrl key.

Options (and Smart Lighting)…

This menu is the go to place if you have some issue with f.lux. At first the customizations don’t make much sense, but when you have used f.lux for several months you know that you need to tweek something.

I’m going to explain what every of the options above do and if it’s usefull for you feel free to use it. I will also tell you about common problems and how to solve them. The good thing about this menu is that it doesn’t close itself automatically every 5 seconds which I find annoying in the f.lux settings panel.

Features and Options

Backwards Alarm Clock (notifications at bedtime)

We already covered what backward alarm clock does, but for the sake of completion if you get notification every hour during the night and you find it annoying uncheck Backwards alarm clock checkbox.

Starting about 9 hours before your wake time, and once every 30 minutes, the backwards alarm clock will calculate how much sleep you will get if you go to bed right now. It will appear about 9 hours before your wake time, and give you a little alert every half hour (it’s a system notifier, so it won’t appear on all older versions of the Mac OS)

The notification on Windows look like this

On the other hand if you want this feature a lot and you like that f.lux will remind you to go to sleep. Checking this checkbox will enable Backwards Alarm Clock

When it’s time for you to go to sleep at night the notification will show. Don’t expect it during the day.

Use wider slider ranges (1200K-9300K)

f.lux default slider ranges are from 1900K to 6500K. The minumim available value by default is 1900K

The maximum available value by default is 6500K

Basically the lower the value of the Color temperature the less blue light is emitted from the screen and the bigger the value the more blue light is emitted from the screen.

6500K is also normal colors of the screen or in the f.lux ui you can see it as Daylight. 1900K is light like this of a candle and this is why you will see it sometimes in the f.lux ui as Candle light.

If you to reduce the blue light even more clicking Use wider slider ranges will allow you to select color temperature down to 1200K and up to 9300K. You can go even lower with keyboard shortcuts down to 800K mode.

Now the minimum value of this sliders is 1200K. 1200K is also called Ember at f.lux and it’s light source like this of an Ember fire.

And the maximum value is 9300K. As I said you can go higher and lower with keyboard shortcuts which I will review later. 9300K has no special name, but it changes the colors to actually increase the blue light emitted from the screen.

Use these hotkeys to control f.lux

Clicking the checkbox above will enable f.lux keyboard shortcuts. Shortcuts seem to be the only way to control the brightness and will also allow you to select color temperature of 800K and up to 100 000K. I have no idea why would you need 100 000K color temperature, but you can.


Will disable f.lux for the next 1 hour. You will get notification like this

The settings panel will also write that f.lux is disabled

And also the tray icon info

When 1 hour has passed f.lux will enable itself again. If you want to force re-enable f.lux you can do this from the settings menu by unckecking disable for 1 hour

You can actually also enable it from here if you don’t want to use the shortcuts

If you press Alt+End again you will get notification that f.lux is back and it will apply it’s color changes again


Alt+PgUp will Increase f.lux brightness. This brightness is not achieved via controlling the backlight, but by moving the white point of the monitor to darker one. This thing is more healthy for the eyes by controlling the backlight, but it will change the screen colors.


Alt+PgDn will Decrease f.lux brightness. This brightness is not achieved via controlling the backlight, but by moving the white point of the monitor to darker one. This thing is more healthy for the eyes by controlling the backlight, but it will change the screen colors.

Be carefull, because if you dim your monitor too much you may not be able to see anything on the screen.

If you try even harder you will be switched to dark room mode and your screen colors will be inverted and red.


Alt+Shift+PgUp will Increase f.lux color temperature by 250K if the color temperature if lower than 6500K and by 500K if the color temperature is more than 6500K.

With this shortcut the color temperature can go all the way up to 100 000K

I’m not sure why the maximum value of daylight seems to be 74%.


Alt+Shift+PgDn will Decrease f.lux color temperature by 250K if the color temperature is lower than 6500K and by 500K if the color temperature is more than 6500K.

With this shortcut the color temperature can go down to 800K which is really nice to the eyes.

On different values there are different messages. For example for 800K it’s Circadian Darkness with 0% Daylight or no blue light at all. Above 1500K the text changes to Winding down

Above 2000K the text shows Staying up late. Note that presing the color temperature shortcuts will unpause f.lux if it’s paused

Over 3000K the text changes to Ready to work and it stays there all the way up to 100 000K

This are the available shortcuts at the moment.

Software mouse cursor when needed (fixes “white cursor”)

If the cursor of the mouse looks like this

When the screen is red or orange and the color temperature is lower checking Software mouse cursor when needed will make the cursor also orange

This is basically a hack which will force software mouse rendering and as any hack it will not work in all cases. What I mean by this is that when you play some games or other fullscreen applications your cursor may dissappear.

So if your cursor dissappears the reason is that you need to uncheck this option and force hardware cursor rendering.

How quickly should transition happen?

f.lux makes slow interpolation when it’s changing colors. At sunset and sunrise it takes f.lux several minutes to go from bright screen to warm. By controlling the tranition speed with this option you can control how fast this transition will happen.

At the moment there are several different transition speeds and I will review them in the next several lines.

Slow: Natural Timing

This is the default f.lux option. Every change to the color temperature will result in gradual interpolation from 1 value to the other. I personally find this a little annoying sometimes, but it’s easy on the eyes. Sometimes this thing uses CPU for the transition, but on more modern PC this thing is basically unnoticeable.

You can also see how the graph is more rounded. This tells you that f.lux is using Natural Timing. Notice how the graph is sharp in the other transition modes.

Medium: Adapt your eyes

With this transition speed when you move the sliders you will see the change instantly. There will be gradual transition on sunrise, sunset and bedtime in order for your eyes to adapt. This transition takes only 1 or 2 seconds. This uses less CPU than the Natural Timing and I find it to be the least annoying and best transition speed.

Notice how much more sharper is the live preview graph. Clicking on the live preview will actually show you the speed of transition from day to night mode.

Very Fast: Gaming

This is instant transition for everything. The point is that f.lux gamma changes sometimes cause lag in games and gaming transition fix should fix your lag. The graph is sharp again and clicking on the preview mode will show you the speed of the transition.

Use monitor data for color calibration

f.lux can use data from your monitor to determine how it’s color looks like. This helps on some monitors which look yellow or green when f.lux is running. If this checkbox is checked f.lux will poll some data out of the monitors that describe their colors better than Windows. This will help you get more accurate colors.

Connected Lighting

Control Philips Hue Lights

If you for some reason happen to have Philips Hue light with this checkbox you can link f.lux color temprerature changes to the hue lights.

When you check this box, you’ll hear a double chime sound. You now need to go to your Philips Hue bridge unit and physically press the sync button on the bridge.

Control Plilips ColorKinetics intelliWhite fixtures on your LAN

Philips ColorKinetics is Philips’ brand of commercial color changing LED systems–if you happen to have a multi-thousand-dollar commercial LED lighting system installed in your home then with this checkbox you can sync f.lux to ColorKinetics.

Post to this URL when f.lux changes

This is something really usefull which maybe no one will use, but I need to explain how to use the f.lux IoT API. Basically if you have some connected device in your home and you are programmer or some kind of hacker here you can write the URL of the server which will recieve f.lux data updates.

To not just talk let me show you my super complicated Python server which will just echo what data f.lux is sending.

import time
import socket
import os

def cls():
    os.system('cls' if os.name=='nt' else 'clear')

serversocket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
serversocket.bind(('localhost', 8000))
serversocket.listen(5) # become a server socket, maximum 5 connections

while True:
    connection, address = serversocket.accept()
    buf = connection.recv(2048)
    if len(buf) > 0:
        print buf
		# clear the screen

Basically Python is programming language and this code will start Echo server on http://localhost:8000/

You can test this sever with this simple Python client.

import socket

clientsocket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
clientsocket.connect(('localhost', 8000))
clientsocket.send('Hello server')

If it’s working enter http://localhost:8000/ to the URL input box in f.lux settings

Now if you have done everything correctly your server will start to recieve data from the running f.lux on your PC. The data looks like this

f.lux is sending POST requests to our server with 2 parameters ct and bri

ct – ct means color temperature and this is the same value that your screen have at the moment. You can use this value to connect your smart lighting to f.lux.

bri – bri means brightness and this is the same value that your screen have at the moment. You can use this value to connect your smart lighting to f.lux.

This seems to be the values that f.lux sends to the server. Feel free to experiment and write your own awesome server.

Poll once a minute

Checking this option will poll the server we created once per minute. You can read a lot about polling on the internet. I’m not going to go into details for the sake of not losing your interest.

Update Automatically

By checking this checkbox f.lux will update itself automatically when there is new version on the f.lux website. You can see the changelog of all f.lux v4 versions here.

Performance Test…

Performance Test is feature of f.lux which will calculate how much your FPS can drop when you use f.lux. The transition of f.lux seems heavy on the machine. When you click the performance test button this window will open

And the screen will start to switch back and forth from bigger to lower color temperature. After a couple of seconds you will see window with the results of the performance test. I tested on my machine with each different transition mode and here are the results

Slow: Natural Timing

Medium: Adapt your eyes

Very Fast: Gaming

I’m not sure what I did wrong, but Medium transition speed seems to have the best average FPS of 54.4 on my machine. Second place is for Slow with 53.5 FPS and third place for gaming with 47.5 FPS.

The gaming mode seems to be the slowest on my machine and I showed you before what is the difference between every mode. Basically changing colors immedially have negative impact on my machine and changing colors for 1 second or Medium: Adapt your eyes transition seems to be the best.


When you finish changing options from the f.lux menu you can click Done to close this window. The settings seems to save even without clicking Done so there is no difference if you would click Done or the close button.

Color Effects


From the Color Effects menu you can choose different color effects. This is basically some color presets which are separated from the f.lux day, night, bedtime schedule and are not connected to it. Color Effects will not change your saved day, night or bedtime settings.

Color Effects will disable the f.lux schedule and they will also not be saved on exit. When you start f.lux again your selected color effects will not be enabled. They are usefull as switching f.lux by hand to some preset settings. The preset are also fixed and not customizable at the moment.

Clicking on the color effect will enable it and clicking on the color effect again will disable it. Switching between some color effects will also disable the old color effect. Some color effects have higher priority than others and Vignette mode is independent of other color effects.

In the next lines I will review what exactly each mode does and how it will change your screen colors.

Movie Move

Movie mode will change your screen color temperature to 4400K. If your screen color temperature was above this value before it will not change anything.

Movie mode will display more accurate blues and skintones. This setting warms up your display, but it preserves shadow detail, skintones, and sky colors better than f.lux’s typical colors.

Darkroom Mode

Darkroom Mode will invert your screen colors and remove all blue and green light. This mode is usefull to decrease the light and blue light emitted from the screen to the maximum. It’s usefull for biohacking your circadian rhythms and your biological clock.

Vignette Mode

Vignette Mode is the only feature in f.lux beta that I think is actually new and cannot be creater just by tweaking your screen gamma. When all other Color Effects are nice to have, but not needed with Vignette mode you can descrease the amount emitted from your screen but preserve the brightness in the center of the screen.

It works by placing transparent vignette overlay over the screen or circle of transparent black color. Note that as shown into the picture menus are not effected by the vignette mode.

Here is my screen with Vignette mode

and here is my screen without Vignette mode

Reduce Eyestrain

Reduce Eyestrain color effect seems like reduces only blue light not also the green this is why it cannot be expressed with color temperature. The reduced blue light seems to be approximately like 5000K, but with green color added.

Blue Sky

Blue Sky color effect will set the color temperature to 100 000K. I would not recommend using this mode. There is no benefit in more blue light. If you actually want to get more blue light it’s better to expose yourself to direct sunlight.

Screen monitor will never replace full spectrum sunlight and I have talked to many doctors which actually recommend reducing blue light even during the day and exposing to sunlight at least 15 minutes per day.

Macular Pigment

Macular Pigment effect will change the screen colors to be something like the color of the macular pigment. It’s something like the Reduce eyestrain effect with green light not reduced, but with more blue light reduced.

Emerald City

Emerald City screen effect will remove red and blue light and will leave only green light. There is no special science behind it just some people may like there screen colors to be green instead of red. This mode will also reduce blue light, but green is closer to blue in the light spectrum than red so red should be preferred.

Himalayan Salt Lamp

Himalayan Salt Lamp color effect will set color temperature to 1400K. This is just preset for color temperature bellow 1900K or the f.lux candle mode. There is maybe again some green light not removed, but basically it’s close to 1400K.

Here is video showing what all different color effects look like

Change color to…

From the Change color menu you can change the color temperature of the screen to different light source presets. Color temperature is measurent for different light sources and it’s measured in Kelvins(K).

You can find many explanation of the color temperature, but to keep the things simple image than the lower the color temperature the less blue light is emitted from the screen.

This thing is usefull to match f.lux to your indoor lighting

Here is also video in which I show how the different settings looks like


From the Disable menu item you can disable f.lux for certain period of time or when certain programs are running. One thing I found is missing is to disable f.lux forever, but I think it’s ok since you can just quit f.lux when you don’t need it. Again this is not the best fix since on the next start of the system f.lux will automatically start so you need to install and uninstall the program.

One more annoying thing is that if you disable f.lux for an hour or until sunrise and you close the program. The next time you start it the settings are not saved. And if you disable f.lux for an hour, close it then start it after 5 minutes the checkbox will be unchecked and f.lux will not be disabled.

Sometimes when using option is also not working correctly, but at least this settings are saved on exit and on the next start they are still active. Now let’s review each of the options in the menu.

Disable for an hour (Alt-End)

With this option or with the shortcut Alt+End you can disable f.lux for 1 hour. Note that this will not be saved if you exit f.lux so you need to select it again if you decide to exit f.lux.

To re-enable f.lux uncheck the checkbox or press Alt+End again

On disabling you will see gradual interpolation to normal colors.

You know that f.lux is disabled when it’s written Disabled in the menu. The color temperature will be 6500K in this case.

Moving the color temperature slider will also re-enable f.lux.

Disable until sunrise

Similar to disable for an hour this option will disable f.lux, but this time until sunrise. Again this will not be saved if you exit f.lux and if you start it again this option will be unchecked.

On disabling you will see gradual interpolation to normal colors.

You know that f.lux is disabled when it’s written Disabled in the menu. The color temperature will be 6500K in this case.

Moving the color temperature slider will also re-enable f.lux.

Disable when using …

While the other 2 options was there also in f.lux 3, disable when using is entirely new feature which was only partially available for Mac OSX until f.lux 4 beta.

With disable when using option, you can disable f.lux when certain program is running. The feature works when the window of the selected program is on focus so it’s not exactly when running, but when on focus.

When you disable a program for the first time and you switch back focus to it you will get notification like this telling you that f.lux is disabled.

To stop disalbing f.lux when the certain program is running just do the same steps again, but this time uncheck the checkbox for when using.

If for some reason this is not working you can find the saved blocked apps in Regedit

Then delete this key

For this to work make sure to first exit f.lux so in the next start it will reload the settings and don’t disable itself when this programs are running.

For more easy deleting I prepared this .reg file

[Download not found]

Download it and then double click it to delete the corresponding regedit key.

Here is also a video showing how the Disable when using … works. It’s really helpfull when you work with Photoshop and with colors

Exit f.lux (v4.29)

Exit f.lux button will stop and quit f.lux. This button will not uninstall f.lux from your system and when you start your PC again f.lux will again start automatically, because it’s in the startup programs list.

Next to the Exit f.lux button you can see the current version which in my case it’s v4.29. Since I’m sure there will be much more changes some options make switch places in the future and some may dissappear. I’m writing this review as of v4.29 of f.lux for Windows.

Tray icon

You can find all of this options also in the tray icon menu. I will not go again in details about what each feature does. You can find the tray icon in the bottom right corner of the screen and right click on it will show the f.lux tray icon menu which is almost the same as the f.lux settings panel menu

Reset settings to default

If you want to reset f.lux settings to default there seems to be no easy way. This is why I made this .reg file which will reset f.lux settings to default.

[Download not found]

Download it, close f.lux and double click it. The next time you start f.lux it will be like the first time you started it.

Lock and Unlock gamma

Remember how when you first installed f.lux how it asked you to write to the registry and changed some settings. After this restart was required. On some monitors this may cause problems and I made this files which will lock and unlock the gamma. Download them, double click them, then restart your PC

To Lock gamma use this file

[Download not found]

To Unlock gamma use this file

[Download not found]

File size and location

f.lux will be installed into the following location


and will take 4.39 MB of your disk space

If you want you can free up some space by deleting setup.exe from the update folder. This file is not used for anything. Deleting anything else will cause the program to crash. Well probably you can also delete the uninstall.exe, but don’t do it 54 KB are not worth not having uninstaller.

If you delete setup.exe you will free 728 KB from your f.lux installation

You can delete this file after every f.lux automatic update.

Installation folder

In the f.lux installation folder you will find several files and folders


Here you can find the color presets in the f.lux ui and some prototion texts.


You will see a PSD file and some other files. f.lux is parsing the .psd file and this is where the ui comes from. If you have experience with Photoshop you can actually change the position of f.lux menus and sliders. You can make the background to be black or other color.


In the update folder there is the latest installation setup.exe downloaded from the server. This file is used for f.lux auto updates.


This is the actual f.lux program which will open the tray icon and the settings window. When you recieve new version this file is replaced. The main logic of f.lux is here and this file loads the psd ui from the runtime folder.


f.lux uninstaller. Start it if you want to delete f.lux from your system.


By default f.lux will automatically start when your computer starts. You can disable this on Windows 10 from the Task Manager. Start Task Manager and select the Startup tab. From here right click f.lux and click Disable.

Now f.lux will not start at startup. If you use version of Windows prior to Windows 10 like Windows 7 or Windows XP you can disable f.lux starting on startup by deleting this regedit key


If you don’t know how to use regedit I made you this file which you just need to double click. Double clicking this file will disable f.lux starting on computer startup

[Download not found]


f.lux works with every Windows operating system including Windows XP, Windows Vista, Windows 7, Windows 8 and Windows 10.


Go to Add or Remove programs and find f.lux

Click Uninstall and follow the uninstaller steps

Clicking Uninstall will start the f.lux uninstaller

When you click uninstall you would be prompted to return Windows to default color settings. This will basically lock the gamma. Click yes if you have some problems with the screen colors

Note that you need to close f.lux before running the uninstaller.

Color calibration

If you have calibrated your monitor with ICC profile f.lux will load it and respect the gamma in it at 6500K and 100% brightness, but if you have calibrated your monitor with other gamma changing application it will not work.

The main Windows Color management settings will work, but software like xcalib or CPKeeper will not work.

f.lux changelog


  • Disable for fullscreen apps (using this allows you to disable one monitor for movies)
  • Disable by app works for 64-bit apps again


  • Disable by app fade timing is improved
  • Cursor is set to hardware mode at exit
  • Minor text edits


  • “Disable by app” only notifies you once per session, not all the time
  • Actual app names are now shown for “disable by app”. (You may have to disable some apps again.)
  • Tray icon now stays hidden when you hide it
  • Some menu text changes


Menus and oopses:

  • Menus are juggled around to help simplify the UI (we are not done yet)
  • Mouse cursor checkbox was broken, now fixed


Some fixes:

  • Software mouse cursor now switches on automatically when colors change, so you keep a hardware cursor during the day (you’ll have to turn it on again in Options)
  • When you don’t enter your location, defaults are quite a bit better
  • Fixes some cases for wake from sleep
  • Some adjustments to vignette mode


This version tries to improve color calibration and fixes some bugs. What’s new:

  • We noticed a lot of laptops are looking very “green-yellow” so we spent some time to figure out what was going on. We were able to pull some data out of the monitors that describe their colors better than Windows does, and so we’re trying to use that data to do more accurate colors now. In the Options menu, there is a checkbox called “Use Monitor Data for Calibration”. We’re turning this on for everyone in this build, so we’d like to know if you think it looks better, or worse!
  • Second, we’ve improved “crushed shadows” by adjusting the response automatically when you dim your screen, so we think photos look a lot better in this new build
  • There’s a new full-screen vignette mode we’re trying out, which manages to show about 60% less light, while still being readable (for some things).
  • Enabling software mouse cursor doesn’t require a logout anymore
  • Bugs fixed on wake from sleep. f.lux should always come back now.
  • Notifiers should never steal keyboard focus, and hotkeys are usable in fullscreen apps/games, because we don’t pop notifiers that kick you back to the desktop

4.21 (a model of you)

We added a lot to this update, so we need your feedback.

In this version, we’re showing everyone a little bit of the way we think about f.lux, giving you some measurements that we think are important. So far, we’ve not really brought “you” and your circadian timing into the f.lux interface.

How light affects you

In this new build, we’ve exposed one of our models of how the light from screens affects your body (based on your screens’ sizes, and using our 5,000-person survey to approximate your viewing distance).

As you adjust settings in f.lux now (or even as you change your laptop’s backlight, which is important), you’ll see one of five common-sense scores for how much light you’re seeing:

  • Bright as Day
  • Ready to Work
  • Staying up Later
  • Winding Down
  • Circadian Darkness

As well, you’ll see a percentage, which we call “% daylight”. It’s a score for how much circadian effect the light you’re seeing might have, compared to broad daylight.

But it’s also important to say, everyone’s a little bit different, so this is just a guideline. You might be more sensitive (especially if you’re under 20) or less sensitive (if you’re over 50, or if you spend a lot of time outdoors).

Is light making you earlier or later? It’s about time too.

Light you see in the morning makes your internal clock “advance” or set itself earlier, and light you see at night makes your clock “delay”. When these adjustments cancel out, your clock stays in about the same place. When you see too much light at night, your clock delays and you want to stay up later.

This new f.lux version indicates the times of day that light is likely to make you later or earlier, so if you open the Preferences screen at night you will see “Light is making you later” and correspondingly “Light is making you earlier” in the morning.

Other changes and fixes in this update

  • Notifications are redesigned, when you use the hotkeys (alt-pgup, alt-end, etc)
  • Some extra support for wide color ranges on Windows 7
  • Gaming mode (safe mode) is removed, because we’ve incorporated everything it does, finally. Use “very fast” transitions if you notice problems
  • We now ask for the “earliest” time you wake up, to clarify what you should do when you have a variable schedule


  • Optimized background performance more (should improve framerate drops), fixed some bugs
  • Added ability to toggle software cursor in the Options (prevent white cursors!) – requires a reboot or logout


  • Default to “slow transition” on purpose! We thought we had done that already, but people who had the old version were getting a fast transition.
  • If you don’t like this, change it in options


  • “Very fast” transition option added for slow GPUs
  • Make custom filters show status when selected
  • Make modes (filters, darkroom) cancel when sliders are moved
  • Disable by app fixes


  • Make wake time work on restart


April 4, 2017

What’s new:

  • Analyzes your displays to show you how bright they are to your body: adjust your backlight and watch!
  • Bedtime mode: warmer light before bed gets you ready for sleep, and works with all kinds of schedules
  • Disable by app (so you don’t forget Photoshop)
  • Backwards alarm clock: reminder not to stay up late
  • Presets to help adjust your settings
  • Color filters for eyestrain and other uses
  • A wider range of color settings
  • New hotkeys to adjust color (alt+shift+PgUp and alt+shift+PgDn)


  • Reduced impact on game framerates
  • Resolution independent interface, for high DPI displays
  • DisplayLink monitors (connected by USB) work in a lot more cases now

Smart Lighting:

  • Hue integration now supports more light types
  • LAN API with support for telling other devices when f.lux changes


Dec 5 2016

This build fixes a number of minor issues with Windows 10 Anniversary Edition:

  • DisplayLink USB monitors no longer cause flashing on the main display
  • Our “NSIS” installer software has been updated due to a security vulnerability
  • Code signing now uses SHA256 to increase security

3.10 bugfixes

Oct 23 2013

This build fixes a number of problems encountered with 3.9:

  • Some users with high-end monitors and video cards experienced persistent flashing. This build fixes most of these bugs. (If you see flashing a few times right after login, we’re still working on it.)
  • f.lux now shows the location dialog when you haven’t set your location and reboot (rather than showing the main window, which confused many people.)
  • Fixes for Philips Hue
  • Clarified text in several places based on user feedback (restarting, asking for location)


Oct 15 2013

Big new cool stuff

  • f.lux can go warmer than 3400K now, down to 2700K. Or even 1200K if you really want it to.
  • Support for color profiles from a hardware calibrator
  • Movie mode. This setting warms up your display, but it preserves shadow detail, skintones, and sky colors better than f.lux’s typical colors. It lasts 2½ hours, which lets you watch most feature films
  • Disable until morning, for late-night crunch mode
  • A new “darkroom” mode, which inverts colors and gets very red
  • A map to help you find your location
  • Hotkeys to dim your display (Alt-PgDn, Alt-PgUp) late at night, so desktop users can dim too
  • A hotkey to disable/enable f.lux quickly: Alt-End
  • If you have a laptop, f.lux gets warmer when your backlight dims, like an incandescent lamp
  • A simple schedule for Philips Hue, so you can f.lux your house

Some more fixes

  • Safe mode for playing video games without hiccups
  • Bugs fixed with Intel chipsets
  • Smoother animations and fading
  • Better support for Windows 7 & 8


June 9 2013


  • better animations, especially for slow transition mode.

If you have f.lux installed, it will update automatically.


June 6 2013


  • settings now persisting correctly
  • fixed website launching menu bug
  • fixed menu problem with setting lighting
  • enhanced Movie Mode to display more accurate blues and skintones.

Final thoughts

f.lux 4 is here and this will be the new f.lux. It has awesome new features and looks like a new program. If you liked this review, you can also see my review of the old f.lux 3.

Thank you very much for reading this article. It’s important for us to try to make digital displays a little more healthy.

Daniel Georgiev – Founder of Iris ?

One thought on “F.lux 4 beta Review (Windows)

  1. Thank you so much for this helpful article- it helped me better understand how f.lux works and was very informative.

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