-the converters or the internal batteries in the EPSUs supply the emergency lighting system.
 An open or short circuit in the control lines causes the emergency lighting to come on. The internal test program in the EPSUs finds defects in the load circuits.

R **ON A/C 051-099, 159-199, 210-299, 303-399,
 Post SB 33-1041 For A/C 051-099,
 The EMER EXIT LT switch 4WL on the overhead panel 25VU controls the emergency lighting system. Self-monitoring circuit breakers 1WL, 2WL and 3WL protect the system from too much current flow. The EMER EXIT LT switch 4WL has three positions, OFF, ARM and ON. Each of these positions gives a discrete ground signal to all EPSUs. The EPSUs also monitor the correct voltage of the AC and DC busbars. When the voltage on these busbars falls below a specified level, the emergency lighting automatically comes on. This is when the EMER EXIT LT switch 4WL is in the ARM position. When only the AC normal busbar fails:
 -
the 28VDC essential busbar supplies the emergency lighting system through

 the 28VDC/6VDC converter in each EPSU.
 When the 28VDC essential busbar fails:

 -
the internal batteries in the EPSUs supply the emergency lighting system.

 When the EMER EXIT LT switch 4WL is in the ON position:

 -
the converters or the internal batteries in the EPSUs supply the emergency lighting system.

 When the LIGHT EMER pushbutton switch and its integral light on the forward attendant panel 120RH are on:

 -
the converters or the internal batteries in the EPSUs supply the emergency lighting system.

 An open or short circuit in the control lines causes the emergency lighting to come on. The internal test program in the EPSUs finds defects in the load circuits.

R **ON A/C 001-049, 051-099, 101-149, 151-199, 201-299, 401-499,
 When the emergency exit hatches are open and the slides are released, the respective overwing emergency lights and the integral lights in the respective escape slide come on. When the passenger/crew doors are open and the slides are armed, the integral lights in the respective escape slide come on.
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 **ON A/C 301-399,
 When the passenger/crew doors or the emergency exit doors are open and the slides are armed, the integral lights in the respective escape slide come on.
 **ON A/C 001-049, 051-099, 101-105, 151-199, 201-228, 301-302,
 In an emergency condition it is possible that the normal cabin emergency-lighting system is not sufficent. This is when smoke enters the cabin. In order to give sufficient illumination of the aisle, exits and emergency exits, a floor-level emergency-lighting system is installed. These emergency lights are a continuous strip of lights, installed at the left side of the aisle. They come on when the emergency lighting system is activated
 **ON A/C 106-149, 229-299, 303-399,
 In an emergency condition it is possible that the normal cabin emergency-lighting system is not sufficent. This is when smoke enters the cabin. In order to give sufficient illumination of the aisle, exits and emergency exits, a floor-level marking-system for the emergency escape-path is installed. The electrical marking system consists of a wall-mounted exit-marking sign at each passenger/crew door and emergency exit. They come on when the emergency lighting system is energized. The photoluminescent marking system consists of a number of flexible photoluminescent strips. They are installed on the floor at both sides of the aisle. 
R  **ON A/C 401-499, 
R R R R R R  In an emergency condition it is possible that the normal cabin emergency-lighting system is not sufficient. This is when smoke enters the cabin. In order to give sufficient illumination of the aisle, exits and emergency exits, a low-level emergency-lighting system is installed. These emergency lights are installed in selected aisle seats and at the passenger exits. They come on when the emergency lighting system is activated. 

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 When the EMER EXIT LT control switch 4WL is in the OFF position and the DC essential busbar 801PP is energized:
 -The EMER EXIT LT OFF annunciator light 5WL in the cockpit comes on.
 **ON A/C 001-049, 051-099, 101-105, 151-199, 201-299,
 You can test the emergency lighting system through the Programming and Test Panel (PTP) 110RH of the Cabin Intercommunication Data System (CIDS). There are two tests :
 -
the BAT test indicates the battery capacity condition of the emergency power-supply units 10WL thru 13WL,

 -
the SYS test indicates the condition of the internal loads, the external loads and the battery charge limiter of the emergency power-supply units 10WL thru 13WL. Internal loads are all electrical loads located inside the cabin and served by these emergency power-supply units. External loads are all electrical loads located outside the cabin and served by these emergency power-supply units.
　
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