Sorry to dig up an old post, but didn't notice the replies and don't like leaving things unfinished!
Strictly speaking a maintained emergency light should be illuminated at material times I would have left it permanently on.
My understanding is that this is certainly true of 'exit boxes' (although I see many that aren't). However, the 'general use' bulkhead EM's we buy are all configurable to be either maintained or non maintained by way of a provided jumper.
Is there a need for emergency lighting or just a night light?
...so in answer to this, the scenario here is (if you can picture it) a rectangular room with a non-maintained bulkhead to the side of the room, adjacent to the main light fitting - in this case a 5ft batten. Entry to the room from a door at the far end to the corridor and a final exit to the outside at the other end.
There are no exit boexes in this room - I suppose because it wasn't considered an escape route due to the fire exit back in the corridor - however, the final exit for the last man out is via this lobby which contains the alarm panel.
In my scenario the 5ft batten is switched from the corridor end of the room. The alarm panel is next to the final exit door. To set the alarm, he has to leave the light on, go to the panel, enter the code, run to the far end of the room to turn the light off and then run all the way back and out the door and vice versa in the morning.
My adjustment means he can enter the lobby from the corridor, turn the main light off which puts the EM into 'maintained' mode in turn giving him enough light at the far end to see hte alarm panel.
The EM was already in situ - so I assume the original designer felt it necessary to have one there. It just happened to be conveniently placed.
Interestingly this is acceptable as per the instructions of the bulkhead (yes, I read them). It states that L1 can be used to provide a switched feed if the light is required to be illuminated.