What is "lightwell"

n. (context architecture English) An open shaft that transmits light from above into a staircase or an inner room

In architecture a lightwell, light well or air shaft is an unroofed external space provided within the volume of a large building to allow light and air to reach what would otherwise be a dark or unventilated area. Lightwells may be lined with glazed bricks to increase the reflection of sunlight within the space.

Lightwells serve to reduce the necessity for electric lighting, add a central space within the building, and provide an internal open space for windows to give an illusion of having a view outside.