(beware, weekend engineering and number pulling here) If you have 250 fixtures, which are each (2) 4' T8 fluorescent bulbs, which would make for (500) 32 watt bulbs, that would be 16 kw, or at $0.13 cpkwhr, would be $1,497/month. But, don't forget, you'd have to cool the heat load generated by the bulbs. 250 fixtures would probably be around a 16 kft datacenter (perhaps smaller). 16 kft in todays datacenters would be about 1.5 mw of usage, between power consumption and HVAC. That'd be $140,400/month. Lighting would account for 1.0% or so. We use a combination of LED and CF (compact fluorescent) for lighting, which with reduced bulb changes (and the associated labor) because of longer live, and the significantly less energy usage, the savings do add up over time. I mean, it adds up in absolute dollars, but perhaps not relative. In our town, the fire folks do not require the emergency lighting to be battery-backed, so long as it is on generator and will not be off for more than 15 seconds. We use an Edison-base style LED fixture, something like http://www.superbrightleds.com/specs/E27-x24_narrow.htm It provides about 15 to 20 watts of equivalent incandescent light, using only 3 watts. Has a neat look too. http://www.nac.net/nac_mmu.jpg
John(damn I've been in a DC with clear floor tiles...why didn't I think of this then?)
How about the concept used in movie theatres? Line the walkways with white LEDs so that people can walk safely.
Far less power, easy to run from small UPS, and use LED exit lights to keep the fire marshalls happy. Even mark the location of fire extinguishers in LEDs.
Customers would be encourages to bring their own florescent panel lamps; rentals would be available for the forgetful.