Stairwell Lighting - Turn it off?

In the middle of the night, in an unoccupied building, do we have to leave the stairwell lights on?  No, but we can't just turn them off completely.  The new life safety code requires a bi-level fixture with a fail-safe occupany sensor. This should pay for itself in about 5 years compared to the usual 24/7 fixture.

Not every city or state uses the same code, of course, but the 2009 Life Safety Code from NFPA says you can turn lights down with a motion sensor but not completely off - and the motion sensor has to be fail safe.

Specifically, NFPA 101 section 7.8.1.2.2 says:   Automatic, motion sensor type lighting switches shall be permitted within the means of egress, provided that the switch controllers are equipped for fail-safe operation, the illumination timers are set for a minimum of 15 minute duration, and the motion sensor is activated by any occupant movement in the area served by the lighting units.

In addition, section 7.8.1.3 says: The floors and other walking surfaces within an exit and within the portions of the exit access and exit discharge shall be illuminated as follows:

During conditions of stair use, the minimum illumination for new stairs shall be at least 10 ft-candles (FC), measured at the walking surfaces. The minimum illumination for floors and walking surfaces, other than new stairs during conditions of stair use, shall be to values of at least 1 ftcandle (FC), measured at the floor.

Translation: you need a special bi-level lighting fixture with built-in fail-safe motion sensor. Vendors are just beginning to make these, so there is a premium price, but a California case study showed savings of 440 kWh per fixture. At a typical 15 cents a kWh, that works out to $66 per year. Our Columbia and Lamar Lighting rep (One Source) says a budget price is about $200 to $250 each, so if $300 installed, then a 5 year payback seems reasonable. Be sure to compare expected savings before making a purchase, as minimum energy use may vary by manufacturer.

Bonus: You can earn rebates from most utilities plus federal energy tax deductions for lighting improvements.

Caveat:  This discussion is all based on NFPA codes, and NFPA does not publish the ubiquitous 2009 International Codes. The International Building Code (IBC) only requires 1 FC at all times. Per Section 1006.2: Illumination level. The means of egress illumination level shall not be less than 1 foot-candle (11 lux) at the walking surface. 

So, if you are strictly governed by IBC, you might get away with 1 FC at all times, unless you wanted higher levels to provide a sense of security.  Keep in mind that this would not comply with the 2009 NFPA Life Safety Code.  So, even if a building inspector allowed it, a fire inspector might not.   Be sure to chat with your local fire marshall before making any decisions (or ask your engineer to help).