Suite au passage sous Ubuntu 16.10 sur mon HP ProBook 650 G2, le rétro éclairage ne fonctionnait plus avec le réglage précédent.
Pour contourner le problème il est possible de passer par le daemon acpid, après détection des touches avec l’outil acpi_listen :
video/brightnessup BRTUP 00000086 00000000 K
video/brightnessup BRTUP 00000086 00000000 K

Il faut donc créer 3 fichiers :
/etc/acpi/hp-probook650g2-backlight.sh

#!/bin/sh

# this directory is a symlink on my machine:
KEYS_DIR=/sys/class/backlight/intel_backlight/
STEP=25
STEPTIME=0.01

test -d $KEYS_DIR || exit 0

MIN=0
MAX=$(cat $KEYS_DIR/max_brightness)
VALOLD=$(cat $KEYS_DIR/brightness)

if [ "$1" = down ]; then
	VAL=$((VALOLD-STEP))
else
	VAL=$((VALOLD+STEP))
fi

if [ "$VAL" -lt $MIN ]; then
	VAL=$MIN
elif [ "$VAL" -gt $MAX ]; then
	VAL=$MAX
fi

if [ "$VAL" -gt "$VALOLD" ]; then
  VALSEQ=$(seq $VALOLD $VAL)
else
  VALSEQ=$(seq $VALOLD -1 $VAL)
fi

for IX in $VALSEQ; do
  echo $IX > $KEYS_DIR/brightness
  sleep $STEPTIME
done

/etc/acpi/events/hp-probook650g2-backlight-down

# /etc/acpi/events/hp-probook650g2-backlight-down
# This is called when the user presses the key brightness 
# down button and calls /etc/acpi/hp-probook650g2-backlight.sh for
# further processing.

event=video/brightnessdown BRTDN 00000087 00000000 K
action=/etc/acpi/hp-probook650g2-backlight.sh down

/etc/acpi/events/hp-probook650g2-backlight-up

# /etc/acpi/events/hp-probook650g2-backlight-up
# This is called when the user presses the key brightness 
# down button and calls /etc/acpi/hp-probook650g2-backlight.sh for
# further processing.

event=video/brightnessup BRTUP 00000086 00000000 K
action=/etc/acpi/hp-probook650g2-backlight.sh up