The exit discharge is the area outside the building, giving the fleeing occupants access all the way to a public way (street, parking lot or alley). In these larger buildings, this "night-light" is required to be lit at all times during darkness when the building is occupied, just the same as the EXIT lights and other egress lighting (night-lights or emergency lights) throughout the building.
A switched porch light would not qualify as this required egress lighting. A photo-cell or time-clock controlled porch light might fit the bill.
All egress and EXIT lighting needs to be on an emergency circuit, or have battery back-up power.