A340 Cabin Emerg Lighting
 

I was reading though this and am wondering about the following:

It says if AC Bus 1 fails to supply minimum cabin lighting then the overhead emergency lights come on automatically.

Is that AC Bus 1-1,1-2 or both?
What exactly is minimum cabin lighting and when does "it" know when that is not being obtained?

Also the cabin emergency lights come on if the DC Ess bus fails-they then run on their own internal batteries. Any idea how long they last?

Grateful if anyone can shed some....um, light on these questions...:} :}

Emergency battery packs have to last for at least 10 minutes.

Think I saw something about 12mins. Anyone have any idea about the rest?

BMM389EC

Correct if the # 1 bus fails the emerg lights come on. but #1 Bus can be/is powered by bus #2 via the isolation breaker and vice versa. eg when one ext power lead is used to power the aircraft on the ground.
To lose this bus you have to have multiple failures isolation breaker fail open and 2 generators fail on the same side or a complete electrical failure.

Please excuse if this is not totally correct as its from memory