Borrowed lighting definition required

[maharg]

For the purposes of emergency lighting can anyone define borrowed lighting for me.
I have seen a number of different Fire Authorities guides and recommendations and these are some of the definitions of Borrowed Lighting I have found:

1. light obtained from another nearby source of emergency lighting.
2. Natural light eg moonlight.
3. Street lighting.

I have done some lux meter readings on the fire route/outside staircase of a 4 storey block of flats.
1/4 moon 1/2 moon and full moon no problems.No moon the centre line is over 1 lux .
No moon and overcast sky part of the centre line drops to .8 lux caused by shadow from the iron girder supports.
This affects 5 x300mm sections of the route .
If I had not taken the readings on an overcast moonless night I would be none the wiser,so how can natural light eg moonlight be acceptable as borrowed light.
thanks

 

[sappaazz]

another defination says 'it is the light entering an interior and otherwise dark room or passage from an adjoining space having windows or skylights.'

so as long as the overcast /no moon night doesnt have any lux, its no longer viable to refer to it as borrowed light

 

[sappaazz]

please not ,
its adjoining not adoining

 

[snowhead]

Guessing only

1. light obtained from another nearby source of emergency lighting. Most likely this.
2. Natural light eg moonlight. You can't guarantee this light being there.
3. Street lighting. You can't guarantee this light being there either, if there is a local power failure.

​

 

[grantr37]

please not ,
its adjoining not adoining

??? :stuart: