What type of building. Are the night lights also going to become egress lights in the event of a power outage? If so, then they need to be spaced to provide the illumination required by OSHA along a path of egress.
If they are just courtesy or walk-thru lighting, then we typically place them near entrances/exits to spaces and near the lighting controls (switches,etc.) so that people can see enough to get to the switches to turn them on. In a wide open space, then space them about every third light or so. Again, just so someone has enough light to get out of the space if their "buddy" turns the lights out on them or an occupancy sensor times out and is the sensor is the type where you actually have to go to a switch to over ride the occupancy sensor to turn the lights back on.
NFPA 101 Section 7.9 is a good place to start, it will point you to the appropriate occupancy sections. Emergency lighting requirements vary depending on the occupancy type. Look in subsection 2.9 of each occupancy section.
