Common halls and stairways. Every common hall and stairway in residential
occupancies, other than in one- and two-family dwellings, shall be
lighted at all times with at least a 60-watt standard incandescent
light bulb for each 200 square feet (19 m2) of floor area or equivalent illumination, provided that the spacing
between lights shall not be greater than 30 feet (9,144 mm). In other
than residential occupancies, means of egress, including exterior
means of egress, stairways shall be illuminated at all times the building
space served by the means of egress is occupied with a minimum of
one footcandle (11 lux) at floors, landings and treads.