Hans de Goede wrote:
most tools simply write directly to /sys/class/backlight, but
xbacklight
relies on the xrandr property (and is the only tool do so AFAICT).
KDE's PowerDevil supports both and prefers XRandR where supported:
https://cgit.kde.org/powerdevil.git/tree/daemon/backends/upower
As you pointed out, the nice thing about the XRandR property is that it does
not require root access, whereas the sysfs interface requires going through
a KAuth/PolicyKit helper to get root (which PowerDevil sets up with a
default policy of "yes" so that all users can use it without a PolicyKit
password prompt). It is sad that most drivers did not bother implementing
it.
Kevin Kofler