When the reading light is set to ON or OFF, the signal is sent directly to the Passenger and Interface Supply Adapter (PISA). An internal transformer rectifier converts the voltage from the 115 VAC normal busbar into 28VDC.Upon activation of the In-Seat control switch, an ARINC 429 signal is sent from the Enhanced Passenger Entertainment System Controller (EPESC) to the Directors. As a result, the Director transmits the signal through the Top Line Data Bus to the DEU-A. Finally, it is relayed to the PISA power supply via a bi-directional serial interface of the Low Voltage Differential Signaling (LVDS) type. The brightness of the passenger reading lights is in correlation to the selected cabin lighting scenario: it depends on the brightness level of the cabin general illumination.The FAP Reading Light Set and Reset pushbuttons enable the manual control of all cabin reading lights, when the aircraft is on ground. To achieve this ground logic control, the Landing Gear Control and Interface Unit (LGCIU) sends the down and compressed landing gear signal to the Directors. Upon power application, the reading light individual operation does not depend on the aircraft being on ground or in flight.Each light is associated to a power supply unit fitted with an internal 115VAC/6VAC transformer. The AC NORMAL BUS 113XP supplies each power supply unit. Each power unit is located in the door.