Questions reference borrowed lighting; 1) if the 'street lighting' is on the same phase as the 'premise lighting' and there is a power failure to the street lighting and/or area, then the premise has no emergency escape lighting.  Is this acceptable when considering designing emergency lighting systems 2) there are different lux levels, required at the points of emphasis within a premise i.e. centre line of an escape route and say, a manual call point.  How is the photometric data gathered and designed around borrowed lighting, when most certainly shadows will form in areas not covered by windows.

Thanks.

Your points are valid and why every revision of BS5266 reduces the acceptance of borrowed lighting more  & more and if you have an escape route and open area that at any time of use would require you to switch the electrical lighting on there is a good chance you will need emergency lighting.

1.  Brad today it’s all about risk assessment so what are the chances of a fire on the premises, the electric supply and external lighting failing at the same time, I would think pretty low consequently an acceptable risk.

2.  If you are accepting borrowed light as acceptable, then you do not require emergency escape lighting therefore photometric data is not necessary.  I would conduct an inspection during the hours of darkness, switch off the lights, if I can find my way about and see what I need see, then emergency lighting is not needed. I accept it cannot be done off plan.

To save any confusion, this is what is now stated in the most recent Emergency Lighting British Standards.

BS 5266-1:2016, Clause 3.1

“Borrowed light
light obtained from an adjacent reliable source that is expected to be available at all material times

NOTE For example, from a local emergency luminaire.”

 

 

 Local emergency luminaire is only an example there would be others, street lighting and daylight for example, so nothing has really changed.

You'd need to consider if you know the street lighting is guaranteed to be on though all the hours needed, or is it switched off at certain times.

Tom, I am in agreement with Paul, Local Authorities in order to save money switch off their Street Lighting, I live in Essex and my Street Lighting is switched off at 02:00 hrs, therefore borrowed lighting in my opinion cannot be relied upon.

It would all depend on how the lights are controlled, the street light out side my house is controlled by a relay and light depending resistor and switches on when it gets dark, off when it gets light. However if as you say the street lighting is not reliable then you would have to ignore it.