The Pantheon in Rome is a great theater for the display of sunlight. It depends for its illumination on a single opening, an oculus located at the center top of its dome, just where one would expect solidity. The domed rotunda is a great space and vessel for light, but daylight is not distributed as well as it might be.
The entry of sunlight is dramatic. The movement of the sun though the sky can be traced as a bright splash that moves across the interior surface of the dome; the impact of this is heightened by the otherwise relatively low light levels. It’s just not that bright inside the rotunda; inside, it feels a little like inhabiting an old sepia photograph. Top lighting can be very efficient as it is capable of distributing light equally from a central point. In this building, the surfaces of the dome redirect some light downward, but these surfaces are not, or no longer highly reflective. Clearly, the ancient marble floor is reflecting a substantial amount of light back onto the rotunda surfaces. But seeing to the walls sometimes requires additional effort, a squint, to focus on the details.
When you step into the Pantheon, you step from the real world into an ideal world, from the everyday world into an idea about the shape of the universe, from the remains of the Roman Empire into the Roman spiritual cosmos. The visual result is one of visual comfort but at seeing through a thin brown veil, or through history, to the drum’s surface of colored marble and shadowed niches, and coffered concrete.