I have a thinkpad (x301) with an external monitor connected via a DisplayPort to HDMI cable. I can control the brightness of the laptop monitor using the keys on the laptop, but I can't work out how to control the brightness of the external monitor.
$ ls /sys/class/backlight/*/brightness /sys/class/backlight/acpi_video0/brightness /sys/class/backlight/intel_backlight/brightness $ cat /sys/class/backlight/acpi_video0/brightness 11 $ cat /sys/class/backlight/acpi_video0/max_brightness 15 $ cat /sys/class/backlight/intel_backlight/brightness 501804 $ cat /sys/class/backlight/intel_backlight/max_brightness 2414340
I can write values into the above and both intel_backlight and acpi_video0 changes the brightness of the laptop monitor.
Does the above mean that there is no way to change the brightness of the external monitor (other than the OSD)?