If in the USA, I believe there is a minimum average light level requirement, like 5 fc or so in most buiding/life safety codes. You need to do some research there. So it needs to be spaced accordingly. If is as much an art as science too.
What type of emergecy lights are you talking aboout? Self-contained emergency lights with battery and charger?
or selective normal lights wired to a generator?or other?
There are some rules of thumb for estimating, for example, self-contained lights/1-50W lamps, if you can figure a light every 50 feet in linear corridor (not more than 25 feet from a point).
I am in the USA. The lights in question are self contained with battery and charger. We are an existing facility. During a safety committee walkthrough, someone brought up the spacing and I did not have a clear answer.
On the blue prints, they seem to be randomly placed, different locations, different heights, etc.
Fire inspectors, electrical contractors and engineering firms with electrical disciplines normally have in their inventory light meters which measure lux or fc. There is a minimum level as the previous responder stated. You may just want to test it out. Also there are numerious lighting programs where you simply place the fixtures on a floor plan and check that the minimum FC is obtained at all areas.
At any rate, you may also want to post this on an electrical or lighting enginnering forum where more of the "sparkies" visit. They might be able to provide some "rules of thumb" for you. Good luck.
I used to do that for a living, and if my memory serves, the standards are located in the Life Safety Code (NFPA 101). You need to check with the AHJ in your area, but in the old days it was paths-of-egress plus places of assembly (and a couple other specific locations) that had to be lit to one footcandle. It might have changed (I'm old).
Good luck with it, and let us know what you find out!
Also Code only requires emergency lightonly path of egress and places of assembly, etc. It is very specific in life safety code NFPA 101. However common sense, building function, occupants familiarity with the building egress paths, protectinng against possible litigation in case of an accident, etc. play role in final locations, and not to forget local AHJ (authority having jurisdiction).
You also want to have emergency lights in electrical and mechanical utitliy rooms.
In short, it is best left to experts in the area, such as good electrical engineering consultants (not necessarily lighting consultants who dwell mostly on esthetics or architectural lighting)
rbulsara gave a a good answer this can be found in the IBC as well as other standards. It is measured at the floor level and must not depend on only one light. See the NEC (2002) section 700.16 for more infomation on the this. Chapter 10 of the IBC(2002) addresses the fc requirements as well as most fire codes.
Need interpretation from an electrical PE or a building inspector in Washington State for the UBC egress path illumination requirements for warehouse aisles. We have exit doors at loading docks at every 200' with exit lights above the door and adjacent ceiling mounted egress light. The egress lighting provides an average one foot candle of illumination at floor level along egress path as defined by the building inspector.
The aisles are about 600' long with cross aisles in the middle for exiting.
Rbulsara said it right. It is as much an art as it is a science. But NFPA 101-The Life Safety Handbook spells it out. 1fc on average throughout public areas which typically are corridors, stairways. Although it really isn't a requirement, mech. and electrical rooms, or public restrooms should have emergency lighting as well. At no point is it to drop below 0.1 fc and the maximum to minimum not to exceed a 40:1 ratio. These readings should be based off of floor level. The NEC, article 620.51 (i think thats where it is at) requires that the emergency lighting source MUST be from the same branch circuit as that of the general lighting circuit. So don't run a new branch or tap off of some other branch for emergency lighting or that will cost you dearly.
The NEC requirement would be for battery unit equipment, so that it knows that the normal source has been lost and will turn on the battery source. That's fine and good, but it is entirely impractical to try to meet the NFPA 101 requirements for more than a few 10's of square feet using battery unit equipment. To truly meet the NFPA 101 requirements would take far too many of the battery units (bug eye units) to be cost effective because their light is not adequately dispersed. For small areas, things like the Bodine battery ballasts can work, but for larger areas the only effective way of meeting the requirements (and there are vast quantities of facilities that don't) is a central system, either a central battery inverter or an emergency generator. In both cases the emergency source would feed conventional lighting on a night light circuit or through other means that assured that the lighting would be on when normal power is not available.
