When is an artificial light source NOT required at the top or bottom stair landing?

An artificial light source is not required at the top or bottom stair landing when each stairway section is adequately lit. This is because building codes typically stipulate that if a stairway is well-illuminated, there is less need for additional lighting at the landings. Proper lighting over each section ensures visibility and safety, reducing the risk of accidents.

With this understanding, the other scenarios don't apply because they either impose lighting requirements regardless of existing light sources (as in the case of constant lighting requirements) or refer to conditions that do not sufficiently meet safety standards set forth by regulations. If there are only four stairs, the presumption may be that they do not necessitate additional lighting, but if the stairs are included in a larger area without adequate lighting, that may still be insufficient. Thus, ensuring each section is already illuminated is the key condition under which artificial lighting at landings is not needed.