# Light

Copyright (C) 2012 - 2014, Fredrik Haikarainen
This is free software, see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE


## Description

Light is a program to control backlight controllers under GNU/Linux, it is the successor of lightscript, which was a bash script with the same purpose, and tries to maintain the same functionality.


## Features

* Works excellent where other software have been proven unusable or problematic, thanks to how it operates internally and the fact that it does not rely on X.
* Can automatically figure out the best controller to use, making full use of underlying hardware.
* Possibility to set a minimum brightness value, as some controllers set the screen to be pitch black at a vaĺue of 0 (or higher).


## Installation

### Arch Linux

If you run Arch Linux, there exists 2 packages;
* [light-git](https://aur.archlinux.org/packages/light-git) - For the absolutely latest version
* [light](https://aur.archlinux.org/packages/light) - For the latest tagged release

I recommend you go with light-git as you might miss important features and bugfixes if you do not.

### Manual

We recommended downloading a versioned tarball from the relases page on
GitHub.  Download and untar the archive:

    tar xf light-x.yy.tar.gz
    cd light-x.yy/
    ./configure && make
    sudo make install

However, should you want to try the latest GitHub source you first need
to clone the repository and run the `autogen.sh` script.  This requires
`automake` and `autoconf` to be installed on your system.

    ./autogen.sh
    ./configure && make
    sudo make install

The `configure` script and `Makefile.in` files are not part of GIT
because they are generated at release time with `make release`.


### Permissions

**Optional:** If you want to use udev rules instead of suid to manage sysfs permissions, you may skip the `make install` step and instead add something like the following to `/etc/udev/rules.d/90-backlight.rules` after copying your binaries:
```
ACTION=="add", SUBSYSTEM=="backlight", RUN+="/bin/chgrp video /sys/class/backlight/%k/brightness"
ACTION=="add", SUBSYSTEM=="backlight", RUN+="/bin/chmod g+w /sys/class/backlight/%k/brightness"
```


## Usage

This application usually has 5 different criteria on flags to use, which are operation modes, value mode, target, field 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 with -v:

* 0: No debug output
* 1: Errors
* 2: Errors, warnings
* 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

You can choose which target to act on:

* -l: Act on screen backlight
* -k: Act on keyboard backlight and LEDs

### Field

As you can not only handle the **brightness** of controllers, you may also specify a field 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). 

**Notice: You _need_ to include the `-s` or `-a` flag on _every_ command you run. The controller setting will _not_ be stored anywhere! If you do not use any of the flags, it will always default to automatic selection.**

### Examples

Get the current brightness in percent

`light -G`, or simply `light`

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`

Try to set the brightness to 0 after that, it will be changed to the minimum 2

`light -Srs "acpi_video0" 0`

Find keyboard controllers

`light -Lk`

Activate `ScrollLock` LED

`light -Sks "input15::scrolllock" 100`

Usually, LEDs only take 0 or 1 in raw value (i.e. for off/on), so you can write

`light -Skrs "input15::scrolllock" 1`

Verify this with `light -v3 -mkrs input15::scrolllock`, you should get a max. brightness of 1