Lightwell

In architecture a lightwell 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 and are a must have for lower ground floors to provide an internal open space for windows to give an illusion of having a view outside.