Red lettering on a black background provides a highly visible warning on your studio door that microphones are live inside. ON AIR or RECORDING legends are available. ON AIR is also available in eight foreign languages. Dimensions: 10" x 5" x 3" Deep. Needs to be installed to house current by a qualified technician, can be wired for either 120V or 240V. Uses 6S6 or 7C7 series lamps.