REDSHIFT(1)

NAME
gammastep - set color temperature of display according to time of day

SYNOPSIS
gammastep [-l LAT:LON | -l PROVIDER:OPTIONS] [-t DAY:NIGHT] [OPTIONS...]

DESCRIPTION
gammastep adjusts the color temperature of your screen according to your surroundings. This may help your eyes hurt less or reduce the risk for delayed sleep phase syndrome if you are working in front of the screen at night.

The color temperature is set according to the position of the sun. A different color temperature is set during night and daytime. During twilight and early morning, the color temperature transitions smoothly from night to daytime temperature to allow your eyes to slowly adapt over a period of about an hour. At night the color temperature should be set to match the lamps in your room. This is typically a low temperature at around 3000K-4000K (default is 4500K). During the day, the color temperature should match the light from outside, typically around 5500K-6500K (default is 6500K). The light has a higher temperature on an overcast day.

In addition to the command-line tool gammastep, the GUI gammastep-indicator provides an alternative interface that shows up as a notification icon in the desktop environment.

OPTIONS

-h  Display help message.

-v  Enable verbose output.

-V  Show program version.

-b DAY:NIGHT
    Screen brightness to apply (between 0.1 and 1.0).

-c FILE
    Load settings from specified configuration file.

-g R:G:B
    Additional gamma correction to apply.

-l LAT:LON
    Your current location, in degrees, given as floating point numbers, towards north and east, with negative numbers representing south and west, respectively.

-l PROVIDER[:OPTIONS]
    Select provider for automatic location updates (Use "-l list" to see available providers).

-m METHOD[:OPTIONS]
    Method to use to set color temperature (Use "-m list" to see available methods).

-o  One-shot mode (do not continuously adjust color temperature). Use this with the -P option to clear the existing gamma ramps before applying the new color temperature.

-O TEMP
    One-shot manual mode (set color temperature). Use this with the -P option to clear the existing gamma ramps before applying the new color temperature.

-p  Print mode (only print parameters and exit).

-P  Reset existing gamma ramps before applying new color effect.

-x  Reset mode (remove adjustment from screen).

-r  Disable fading between color temperatures.

-t DAY:NIGHT
    Color temperature to set at daytime/night.

The neutral temperature is 6500K. Using this value will not change the color temperature of the display. Setting the color temperature to a value higher than this results in more blue light, and setting a lower value will result in more red light.

Default temperature values:

    Daytime: 6500K, night: 4500K

CONFIGURATION FILE
A configuration file with the name config.ini can optionally be placed in ~/.config/gammastep/ (if the environment variable XDG_CONFIG_HOME is undefined) or ${XDG_CONFIG_HOME}/gammastep/ (if XDG_CONFIG_HOME is defined). The file has standard INI format. General program options are placed under the general header, while options for location providers and adjustment methods are placed under a header with the name of that provider or method. General options are:

temp-day = integer
    Daytime temperature

temp-night = integer
    Night temperature

fade = 0 or 1
    Disable or enable fading between color temperatures.

brightness-day = 0.1-1.0
    Screen brightness at daytime

brightness-night = 0.1-1.0
    Screen brightness at night

elevation-high = decimal
    The solar elevation in degrees for the transition to daytime

elevation-low = decimal
    The solar elevation in degrees for the transition to night

dawn-time = HH:MM[-HH:MM]
    The custom time interval for the transition from night to day in the morning. When specified, the solar elevation will not be used to determine the current daytime/night period. If this option is set, dusk-time must also be specified.

dusk-time = HH:MM[-HH:MM]
    The custom time interval for the transition from day to night in the evening. When specified, the solar elevation will not be used to determine the current daytime/night period. If this option is set, dawn-time must also be specified.

gamma = R:G:B
    Gamma adjustment to apply (day and night)

gamma-day = R:G:B
    Gamma adjustment to apply at daytime

gamma-night = R:G:B
    Gamma adjustment to apply at night

adjustment-method = name
    Select adjustment method. Options for the adjustment method can be given under the configuration file heading of the same name.

location-provider = name
    Select location provider. Options for the location provider can be given under the configuration file heading of the same name.

Options for location providers and adjustment methods can be found in the help output of the providers and methods.

EXAMPLE
Example for Copenhagen, Denmark:

    $ gammastep -l 55.7:12.6 -t 5700:3600 -g 0.8 -m randr -v

An example configuration file with the same effect as the above command line:

    [general]
    temp-day=5700
    temp-night=3600
    gamma=0.8
    adjustment-method=randr
    location-provider=manual
    [manual]
    lat=55.7
    lon=12.6

HOOKS
Executables (e.g. scripts) placed in folder ~/.config/gammastep/hooks will be run when a certain event happens. The first parameter to the script indicates the event and further parameters may indicate more details about the event. The event period-changed is indicated when the period changes (night, daytime, transition). The second parameter is the old period and the third is the new period. The event is also signaled at startup with the old period set to none. Any dotfiles in the folder are skipped.

A simple script to handle these events can be written like this:

    #!/bin/sh
    case $1 in
        period-changed)
            exec notify-send "Gammastep" "Period changed to $3"
    esac

AUTHOR
gammastep was written by Jon Lund Steffensen <jonlst@gmail.com>, and is now maintained by Cameron Nemo <cam@nohom.org>.

Both gammastep and this manual page are released under the GNU General Public License, version 3.

BUGS
Please report bugs to <https://gitlab.freedesktop.org/CameronNemo/gammastep/issues>

KNOWN ISSUES
gammastep will not affect the color of your cursor when your graphics driver is configured to use hardware cursors. Some graphics drivers have an option to disable hardware cursors.