Build command for setting the brightness of the led.
        :param brightness: Value to set (0.0-1.0).
        :return: The command.

def brightness(self, brightness):
        """
        Build command for setting the brightness of the led.
        :param brightness: Value to set (0.0-1.0).
        :return: The command.
        """
        return self._build_command(0x4E, self.convert_brightness(brightness),
                                   select=True, select_command=self.on())