There are 2 LEDs on the Core-1684JD4 board:

Color Location Symbol Description
Yellow Up DIY_LED User controls
Green Down WORK_LED Power on

Example command to control LED light state (requires root privileges):

# yellow light on
echo 1 >/sys/class/leds/DIY_LED/brightness
# yellow light off
echo 0 >/sys/class/leds/DIY_LED/brightness

# green light on
echo 1 >/sys/class/leds/WORK_LED/brightness
# green light off
echo 0 >/sys/class/leds/WORK_LED/brightness