An oculus can be used in an exterior canopy as a way to brighten an entryway. The location of the light beam cast by the oculus will shift throughout the day as the sun moves across the sky.
An oculus is also a great way to bring light deep into the interior of a home, especially when it's located above a vertical element, such as a stairway.
An oculus is a great way of introducing a shaft of light that enlivens a space.
It may also provide a glimpse of the sky above.