The Professors of Light and Darkness were the joint deans of the School of Light and Darkness in Sanctaphrax. The Professor of Light was in charge of light-studies, and the Professor of Darkness was in charge of darkness-studies.
The Old Professors of Light and Darkness
The Professors of Light and Darkness during the Quint and Twig trilogies (whose real names were never revealed) met each other at an early age and became close friends, drawn together by their shared fascination of luminosity. So strong was their bond that they began to mirror each other's actions and personalities, even assuming each other's physical characteristics. Linius Pallitax, the Most High Academe of Sanctaphrax, elected them both to the position of Next-Most High Academe, and they assumed many of the ceremonial duties of the great floating city, such as inspecting the stormphrax in the Treasury once every year on Treasury Day.
At the beginning of The Winter Knights, the Professors of Light and Darkness became joint Most High Academes, after the death of Linius Pallitax. Later on, Vilnix Pompolnius convinced the academics of Sanctaphrax that the Professors of Light and Darkness were inept, and persuaded them to elect him Most High Academe in their place.
The Professor of Light accompanied Cloud Wolf on a stormchasing voyage, but broke his neck while abandoning ship in the Twilight Woods. Because of the Twilight Woods' effects, the Professor of Light neither died nor felt any pain. However, he died much later halfway through the journey across the Mire.
After Twig stabilized Sanctaphrax with fresh supplies of Stormphrax, Vilnix Pompolnius was dethroned, and the Professor of Darkness resumed his duties as Most High Academe. However, when the Mother Storm arrived and Sanctaphrax had to be unchained, the professor, unwilling to let go of the great floating city, seized the severed Anchor Chain and floated off into Open Sky.
The New Professors of Light and Darkness
During the Rook trilogy, the new Professors of Light and Darkness were Ulbus Vespius and Tallus Penitax. These two scholars fled the Tower of Night when the schemes of Orbix Xaxis became too evil for their tastes, and joined the Librarians Academic. Later on, they joined the council of the Free Glades when the Librarians relocated there.