code: def led_changed(self, addr, group, val):
          
          _LOGGER.debug("Button %d LED changed from %d to %d",
                        self._group, self._value, val)
          led_on = bool(val)
          if led_on != bool(self._value):
              self._update_subscribers(int(led_on))
docs: Capture a change to the LED for this button.