tried echo,xrandr and even xbacklight couldn't reduce backlight of my screen. Can anyone suggest any other way?
If you want to change the screen brightness in Ubuntu (I can’t change it using the keyboard shortcuts or the Ubuntu Power Management menu), open a terminal and execute the following:
sudo setpci -s 00:02.0 F4.B=xx
Where xx is the desired brightness in hex ranging from 0 (brightest) to FF (no brightness at all). I usually change it to E0 when working on battery.
One such program that can dim a display which does not have backlight control built in is a program called Redshift
Redshift's purpose is to warm the colours of your screen during the night to make late-night computer use easier on your eyes.
It also has screen dimming functionality built into the app that does not require a dimm-able screen backlight, and if you so wish, you can use it purely for this purpose by disabling the colour-warming.
NOTE: To install redshift, you must have enabled Ubuntu's Community-maintained free and open-source software repository codenamed 'universe'
In Ubuntu 14.04, this should be enabled by default. If you have for some reason disabled the universe repository, you can follow the instructions in this thread to re-enable them!
To install and configure Redshift on Ubuntu 14.04 for the purpose of dimming your screen:
Enter the following command into a terminal window (open the terminal window by pressing ctrl+alt+t)
sudo apt-get install redshift-gtk
Go to latlong.net and find the appropriate latitude and longitude for your city. Then enter the following command into a terminal window using the location you find as lat:lon.
(you can skip this step if you don't want the brightness to change based on whether it is currently night or daytime)
redshift -l lat:lon
e.g. for Sydney, Australia you would enter:
redshift -l -33.867:151.207
sudo nano ~/.config/redshift.confin a terminal window to create a config file for redshift, this file is where you are going to set the brightness and temperature that Redshift is going to set your screen at.
Documentation for this file is sparse, but a full example can be seen on the project's website
You are going to want to type the following into the config file:
If you wish to further customize the config, here is my config file with comments to explain each setting:
; Global settings for redshift
; Set the day and night screen temperatures
; Enable/Disable a smooth transition between day and night
; 0 will cause a direct change from day to night screen temperature.
; 1 will gradually increase or decrease the screen temperature
; Set the screen brightness. Default is 1.0
; It is also possible to use different settings for day and night since version 1.8.
; Set the screen gamma (for all colors, or each color channel individually)
; Set the location-provider: 'geoclue', 'gnome-clock', 'manual'
; type 'redshift -l list' to see possible values
; The location provider settings are in a different section.
; Set the adjustment-method: 'randr', 'vidmode' ; type 'redshift -m list' to see all possible values ; 'randr' is the preferred method, 'vidmode' is an older API ; but works in some cases when 'randr' does not. ; The adjustment method settings are in a different section. ;adjustment-method=randr
; Configuration of the location-provider: ; type 'redshift -l PROVIDER:help' to see the settings ; ex: 'redshift -l manual:help' [manual] lat=-26.658006 lon=153.053269
; Configuration of the adjustment-method ; type 'redshift -m METHOD:help' to see the settings ; ex: 'redshift -m randr:help' ; In this example, randr is configured to adjust screen 1. ; Note that the numbering starts from 0, so this is actually the second screen. [randr] screen=0