[Unit]
Description="Turn keyboard backlight on/off based on light sensor"

[Service]
Type=exec
Environment=SENSOR=/sys/bus/iio/devices/iio:device2/in_illuminance_raw
WorkingDirectory=/sys/class/leds/tpacpi::kbd_backlight/
ExecStart=bash -c "(( $(cat ${SENSOR}) < 1500 )) && echo 1 > brightness || echo 0 > brightness"

[Install]
WantedBy=multi-user.target