Settings available via the OSD (On-Screen Display) panel can usually also be managed via DDC. DDC can control brightness, contrast, inputs, etc on supported monitors. When using this method, you need to use lspci first to find out where your graphic card is.ĭDC/CI (Display Data Channel Command Interface) can be used to communicate with external monitors implementing MCCS (Monitor Control Command Set) over I2C. Not all of the graphic cards support this method. It means you adjust the backlight by manipulating the hardware directly, which can be risky and generally is not a good idea. Intel Mobile 945GME ), it is possible to set the register of the graphic card to adjust the backlight. Tip: To set the backlight depending on power state, see Power management#Using a script and an udev rule and use your favourite backlight utility in the script. etc/udev/rules.d/les ACTION="add", SUBSYSTEM="backlight", RUN+="/bin/chgrp video $sys$devpath/brightness", RUN+="/bin/chmod g+w $sys$devpath/brightness" To allow users in the video group to change the brightness, a udev rule such as the following can be used: # echo 5 > /sys/class/backlight/acpi_video0/brightnessīy default, only root can change the brightness by this method. Attempting to set a brightness greater than the maximum results in an error. The brightness can be set by writing a number to brightness.
$ cat /sys/class/backlight/acpi_video0/max_brightness 15 The maximum brightness can be displayed by reading from max_brightness, which is often 15. $ ls /sys/class/backlight/acpi_video0/ actual_brightness brightness max_brightness subsystem/ uevent The directory contains the following files and subdirectories: If you use an Intel card, simply replace acpi_video0 with intel_backlight in the examples. In the following examples, acpi_video0 is used. In the case of an Intel card, the directory is called intel_backlight. In this case, the backlight is managed by an ATI graphics card. The name of the directory depends on the graphics card model. An interface to this module is provided via a sysfs(5) directory at /sys/class/backlight/. The power level can often be controlled using the ACPI kernel module for video.
The brightness of the screen backlight is adjusted by setting the power level of the backlight LEDs or cathodes. In this case, perceived screen brightness can be adjusted with a PWM control (not implemented in the Linux kernel) or via software color correction. Note: Since OLED screens have no backlight, brightness cannot be controlled by changing backlight power on laptops equipped with an OLED screen.
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