Difference between revisions of "Light"

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[[Category:Power management]]
#REDIRECT: [[Backlight#Backlight utilities]]
Light is a program used to easily control a screens backlight-controllers. It is the successor of ''LightScript'', and is also its official C-port.
== Features ==
* Works excellent where other software has been proven to be unusable or problematic, thanks to how it operates internally and to the fact that it does not rely on X.
* Can automatically figure out the best controller to use, making full use of underlying hardware. (Does not use vendor-specific ACPI or even ACPI at all, but uses driver implementations. This is against recommendations but this is what has been proven to work best when all else fails).
* Possibility to set a minimum brightness value, as some controllers set the screen to be pitch black at a value of 0 (or higher).
== Installation ==
Light has 2 different packages on the AUR, {{AUR|light}} for the latest tagged version, or {{AUR|light-git}} for the absolutely latest version with the most features. Patches are frequently committed to the git repository so it is recommended to use the {{AUR|light-git}} package to make sure you have the latest features/bug-fixes.
== Usage ==
This application usually has 4 different criteria on flags to use, which are operation modes, value mode, target and controller mode. Flags from these different modes can never be used in conjunction, but all of them do not always have to be specified (although it is recommended to do so for verbosity).
{{Note|This application will only print errors if you are using it incorrectly. If something goes wrong, and you can't figure out why, try setting the verbosity flag:
*-v 0: No debug output
*-v 1: Errors
*-v 2: Errors, warnings
*-v 3: Errors, warnings, notices}}
=== Operation modes ===
The operation modes describe '''what''' you want to do.
*-G: Which '''reads/gets''' brightness/data from controllers/files
*-S: Which '''writes/sets''' brightness/data to controllers/files
*-A: Which does like -S but instead '''adds''' the value
*-U: Which does like -S but instead '''subtracts''' the value
*-O: Save the current brightness for later use (usually used on shutdown)
*-I: Restore the previously saved brightness (usually used on boot)
*-L: List the available controllers
When used by themselves operate on the brightness of a controller that is selected automatically. S, A and U needs another argument -- except for the main 4 criteria -- which is the value to set/add/subtract.  This can be specified either in percent or in raw values, but remember to specify the value mode (read below) if you want to write raw values.
=== Value modes ===
The value mode specify in what unit you want to read or write values in. The default one (if not specified) is in percent, the other one is raw mode and should always be used when you need very precise values (or only have a controller with a very small amount of brightness levels).
*-p: Percent
*-r: Raw mode
Remember, this is the unit that will be used when you set, get, add or subtract brightness values.
=== Target ===
As you can not only handle the '''brightness''' of controllers, you may also specify a target to read/write from/to:
*-b: Current brightness of selected controller
*-m: Maximum brightness of selected controller
*-c: Minimum brightness (cap) of selected controller
The minimum brightness is a feature implemented as some controllers make the screen go pitch black at 0%, if you have a controller like that, it is recommended to set this value (in either percent or in raw mode). These values will be saved in raw mode though, so if you specify it in percent it might not be too accurate depending on your controller.
=== Controller modes ===
Finally, you can either use the built-in controller selection to get the controller with the maximum precision, or you can specify one manually with the -s flag. The -a flag will force automatic mode and is default. Use -L to get a list of controllers to use with the -s flag (to specify which controller to use).
=== Examples ===
Get the current brightness in percent
light -G
Increase brightness by 5 percent
light -A 5
Set the minimum cap to 2 in raw value on the acpi_video0 controller:
light -Scrs "acpi_video0" 2
{{Tip|These commands can be bound to keyboard keys as described in [[Extra keyboard keys in Xorg]].}}
== Bugs/Feedback ==
Please give bugs/feedback directly on the AUR-page comments.

Latest revision as of 14:05, 4 January 2015