I do:
cat /sys/class/backlight/intel_backlight/brightness
851
I try:
echo 100 > /sys/class/backlight/intel_backlight/brightness
And I get an input/output error.
If I load plasma libraries by opening up dolphin, then it works fine. But i'd rather be able to do without plasma/kde libraries.
The easiest method to control backlight is using ACPI interface
I useacilight (https://gitlab.com/wavexx/acpilight) to control backlight.
maybe you need to follow the setup instruction mentioned in the gitlab of acpilight.
On my laptop, I added a toolbar (XFCE4) containing four nice icons to adjust the screen brightness:
sudo pacman -Sy acpilight
(a backward-compatible xbacklight replacement)
Then, I created 4 or 5 launchers with nice icons in a toolbar:
xbacklight =1
xbacklight =10
xbacklight =50
xbacklight =100