This works on my ar300m (including turning off the power led) but it should work on any of them:
find /sys/devices/platform/leds-gpio/leds/ ! -path ‘usbpow’ -name brightness -exec sh -c ‘echo 0 > {}’ ;
to turn them back on (except for power) I use:
/etc/init.d/led start
If you want to turn the power led back on change 0 to 255 in the first find command above.
I put these in cron to turn them off at night and back on during the day.