Every habitable room shall be provided with natural light complying with the provisions of this subchapter.
(a) Natural light, when required, shall be provided by windows, skylights, monitors, glazed doors, transoms, fixed lights, jalousies or other natural-light transmitting media. Such sources shall not be located in recesses having a width of less than six feet, and such sources shall not be located so as to create a habitable room whose depth exceeds thirty feet, except in dwelling units of group one construction containing more than three habitable rooms. Such sources, except as provided in subdivision (b) of this section, shall face or open upon the sky or upon a public street, space, alley, park, highway, or right of way, or upon a yard, court, plaza, or space above a setback, when such yard, court, plaza, or space above a setback is located upon the same lot and is of the dimensions required by the applicable provisions of the zoning resolution. Where dwelling units in buildings or spaces classified in occupancy group J-1 or J-2 are located in a cellar or a basement such dwelling unit or units shall have at least one-half of their height and all of their window surfaces above every part of an "adequate adjacent space". Such "adequate adjacent space" shall be open to the sky and shall be a continuous surface area outside the dwelling unit or units not less than thirty feet in its least dimension and abutting at same level or directly below every part of the exterior walls of such dwelling unit or units. Such "adequate adjacent space" shall include only spaces which are located on the same lot or plot as the building or on a public street, space, alley, park, highway or right of way and the level of such areas which abut or adjoin the habitable room at least shall be six inches below the window sills of any windows.
(b) Natural light sources may face or open upon an enclosed or partially enclosed balcony or space above a setback when such balcony or space faces upon a public street, space, alley, park, highway or right of way or upon a yard, court, plaza, or space above a setback, when such yard, court, plaza, or space above a setback is located upon the same lot and is of the same dimensions required by the applicable provisions of the zoning resolution, the maximum depth of any habitable room is at most thirty feet measured from the outer face of the wall forming the partial or full enclosure of the balcony or space, the enclosure of the balcony or space is not more than one story in height, and the balcony or space complies with either of the following:
(1) The front of the balcony or space above a setback has an opening to the outer air whose area is equal to at least seventy-five percent of the floor surface area of such balcony or space.
(2) The front of the balcony or space above a setback may be completely enclosed when the building is of group one construction provided the outer enclosing walls are glazed with clear plate glass or with plastic equivalent complying with subdivision (e) of section 27-331 of article four of subchapter five of this chapter and such glazed wall area is equal to at least fifty percent of the interior walls enclosing such balcony or space and at least fifty percent of the required glazed area is openable and no window from any bathroom, watercloset compartment, or kitchen whose area is fifty-nine square feet or less opens on such balcony or space.
(b) Natural light sources may face or open upon an enclosed or partially enclosed balcony or space above a setback when such balcony or space faces upon a public street, space, alley, park, highway or right of way or upon a yard, court, plaza, or space above a setback, when such yard, court, plaza, or space above a setback is located upon the same lot and is of the same dimensions required by the applicable provisions of the zoning resolution, the maximum depth of any habitable room is at most thirty feet measured from the outer face of the wall forming the partial or full enclosure of the balcony or space, the enclosure of the balcony or space is not more than one story in height, and the balcony or space complies with either of the following:
(1) The front of the balcony or space above a setback has an opening to the outer air whose area is equal to at least seventy-five percent of the floor surface area of such balcony or space.
(2) The front of the balcony or space above a setback may be completely enclosed when the building is of group one construction provided the outer enclosing walls are glazed with clear plate glass or with plastic equivalent complying with subdivision (e) of section 27-331 of article four of subchapter five of this chapter and such glazed wall area is equal to at least fifty percent of the interior walls enclosing such balcony or space and at least fifty percent of the required glazed area is openable and no window from any bathroom, watercloset compartment, or kitchen whose area is fifty-nine square feet or less opens on such balcony or space.
Required sources of natural light shall have an aggregate transmitting area of at least ten percent of the floor area of the room or space served and where an enclosed or partially enclosed balcony or space above a setback complying with section 27-733 of this article intervenes, the required sources of natural light shall have an aggregate transmitting area of at least ten percent of the combined floor area of such room and the portion of the balcony or space directly adjoining and in front of such room. Each required source shall have a minimum transmitting area of twelve square feet and only that area of the light source above thirty inches from the finished floor may be considered as providing the natural light required in any space.