One thing I would like to add to this thread, is the fact that if the lights suddenly go out in a place, you can bank on the fact that people will panic.
Most people are only in a store to buy things and then leave, most would not know how to retrace thier steps to get out of the place, couple that with the fact that most buildings these days are of tilt-slab construction and often don't have windows, therefore negating any natural light inside the building.
Emergency lighting systems here seem to be so poor in providing enough light to actually be effective that I reckon that an LED strip or something similar should be continuously illuminated.
Having been a FF for some years, the best thing you can do if you get lost, is sink back down to ground level.
I ran out of air from my BA (Breathing Apparatus) set once, there is a 2ft space under the smoke that has breathable air.
Some LED indicators would have been really helpful.
