Updated.

polybar/scripts/brightnessctl.sh

@@ -0,0 +1,16 @@
+#!/bin/bash
+BRIGHTNESS_VALUE=`brightnessctl | grep -o "(.*" | tr -d "()"`
+BRIGHTNESS_NR=${BRIGHTNESS_VALUE//%}
+
+if [ $BRIGHTNESS_NR -lt 20 ]; then
+	BRIGHTNESS_ICON=''
+elif [ $BRIGHTNESS_NR -lt 50 ]; then
+	BRIGHTNESS_ICON=''
+elif [ $BRIGHTNESS_NR -lt 80 ]; then
+	BRIGHTNESS_ICON=''
+else
+	BRIGHTNESS_ICON=''
+fi
+
+echo "$BRIGHTNESS_ICON $BRIGHTNESS_VALUE"
+