If you use laptop-mode-tools, you will need the following in /etc/laptop-mode/conf.d/lcd-brightness.conf to configure the brightness of the screen:

BATT_BRIGHTNESS_COMMAND="echo 3000"
LM_AC_BRIGHTNESS_COMMAND="cat /sys/class/backlight/intel_backlight/max_brightness"
NOLM_AC_BRIGHTNESS_COMMAND="cat /sys/class/backlight/intel_backlight/max_brightness"
BRIGHTNESS_OUTPUT="/sys/class/backlight/intel_backlight/brightness"

and the following in /etc/laptop-mode/conf.d/cpufreq.conf to use the correct CPU governors:

BATT_CPU_GOVERNOR=powersave
LM_AC_CPU_GOVERNOR=performance
NOLM_AC_CPU_GOVERNOR=performance