Turn led off on RaspberryPi 3B

To turn off the power led of a Raspberry PI 3B add the following lines to /boot/config.txt under the [all] section and reboot your PI.

# Disable power led
dtparam=pwr_led_trigger=default-on   # The default
dtparam=pwr_led_activelow=off
See https://github.com/raspberrypi/firmware/issues/1742 why on recent kernel versions the first line is needed.