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 sixty (60) watt standard incandescent light bulb for each two hundred (200) square feet (19 m²) of floor area or equivalent illumination, provided that the spacing between lights shall not be greater than thirty (30) feet (9144 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 (1) footcandle (11 lux) at floors, landings and treads. (402.2)