Cal. Civ. Code § 217

  § 217. Lighting and ventilation of public halls and stairs. 1.  In
every tenement erected after April twelfth, nineteen hundred one, which
exceeds four stories in height or is occupied by three families or more
on any story, every public hall shall have at least one window opening
directly upon a street, yard or court. Such window shall be located at
the end of the hall and at right angles to its length, with an
additional window in each thirty feet of hall or fraction thereof beyond
the first sixty feet from such end window if the tenement was erected
after April eighteenth, nineteen hundred twelve; or, if the window is
not thus located at the end of the hall, there shall be at least one
window opening directly upon a street, yard or court in every twenty
feet of the length of the hall or fraction thereof, measured from one
end of hall; but the foregoing provisions shall not apply to that
portion of an entrance hall between the entrance and the first flight of
stairs if the entrance door contains five square feet or more of glazed
surface.
  2. When the length of any recess or return off of a public hall in
such a tenement does not exceed twice its width, no window shall be
required therein. But wherever the length of a recess or return exceeds
twice its width there shall be an additional window or windows meeting
the requirements for a separate public hall.
  3. Except as provided in subdivision four, a tenement erected after
April twelfth, nineteen hundred one, which is four stories or less in
height and occupied by not more than two families on any story shall
either have windows in its public halls as above provided or a stairwell
twelve inches or more in width extending from the entrance story to the
roof. In such a tenement, except as provided in subdivision four, every
entrance door shall contain five square feet or more of glazed surface,
and all doors leading from the public halls shall be provided with
translucent glass panels five square feet or more in area for each door
and fixed transoms of translucent glass over each door.
  4. Neither such windows nor such a stairwell shall be required in
cities of one million or more population in tenements which do not
exceed three stories in height or fifty-five feet in depth and which are
occupied by not more than one family on any story and in which the
stairs descend in a straight and continuous run from the top story to
the entrance story with proper landings at each story. Such tenements
shall not be required to have glass panels or transoms in the doors
leading from the public halls.
  5. In every public hall that is provided with a window or windows in a
tenement erected after April twelfth, nineteen hundred one, at least one
such window shall be at least two feet six inches wide and five feet
high.
  6. In every such tenement there shall be provided, at every floor
level, a window opening upon a street, yard, court or space above a
setback to light and ventilate every stair. Every such required window
shall be of the size required by subdivision five, except that a window
opening upon a street need be only four feet high. On the top story a
ventilating skylight of the same dimensions shall be accepted in lieu of
a window for that story.
  7. In every such tenement there shall be in the roof, directly over
each stairwell, a ventilating skylight provided with ridge ventilators
having an opening of at least forty square inches, or provided with
fixed or movable louvres. The roof of every such skylight shall have at
least twenty square feet of glazed surface. If the stairs and public
halls are not provided at each story with windows opening directly to
the outer air, the skylights shall be provided with ridge ventilators
and also with fixed or movable louvres or movable sashes.
  8. A sash door shall be deemed the equivalent of a window for the
purposes of this section if it contains the amount of glazed surface
prescribed for such windows.
  9. In all old-law tenements the public halls and stairs shall be
provided with such skylights, ventilators, windows in bulkheads or other
means of lighting and ventilation as may be deemed practicable by the
department.
  10. All skylights installed in old-law tenements after April
eighteenth, nineteen hundred twenty-nine, shall be provided with ridge
ventilators having an opening of at least forty square inches and also
with fixed or movable louvres or with movable sashes. They shall be of
such size as may be determined to be practicable by the department, and
the roofs of such skylights shall be glazed with plain glass equipped
with suitable wire screen above and below.
  11. Whenever a public hall in any old-law tenement four stories or
more in height is not light enough in the daytime to permit a person to
read in every part thereof without the aid of artificial light, every
door at the end of such hall or opening therefrom into a room shall have
a wire glass panel or panels of an aggregate area of at least four
square feet; or in lieu thereof such hall may be lighted by a window or
windows opening upon a street or upon a lawful yard, court or shaft,
with the plane of each such window at right angles to the length of the
hall. In any such tenement any public hall or stair which is not
provided with a window opening directly upon a street or yard and which
is not sufficiently lighted in the opinion of the department shall be
provided by the owner with artificial light, which shall be kept burning
at all times.
  12. Any part of a public hall that is shut off from any other part of
such hall by a door or doors shall be deemed a separate hall for the
purposes of this section.