+ <filename>/var/lib/systemd/backlight/</filename>. During
+ loading, if udev property
+ <option>ID_BACKLIGHT_CLAMP</option> is not set to
+ false value, the brightness is clamped to a value of
+ at least 1 or 5% of maximum brightness, whichever is
+ greater. This restriction will be removed when the
+ kernel allows user space to reliably set a brightness
+ value which does not turn off the display.</para>