To combine the unity of a central plan with the direction a church needs, plan the space as an oval, set across the axis to widen the view of the altar, or along it to lead the eye towards it.
Light from a hidden source
Light the climax of a Baroque interior (the altar or the dome) from windows the visitor cannot see, so that it seems to glow of itself.
In Bernini’s Cornaro Chapel a window hidden above the altar lights the sculpture of St Teresa from behind gilded rays; at Sant’Andrea the altar chapel has its own concealed lantern, and the main dome is lit from its lantern and from windows set low in its base. The nave is kept relatively dim, so that light marks the goal of the visitor’s movement. The technique came from the theatre, where Bernini also worked, and was taken up throughout Catholic Europe.
Related rules
Divide the inside of a dome into coffers that shrink in step with the meridians as they rise, so that their perspective deepens the dome and draws the eye to the light of the lantern.
To set a round dome on a square bay, imagine a sphere passing through the four corners of the square; cut it by the four vertical planes of the sides and by the horizontal plane of their crowns. The four spherical triangles left in the corners are the pendentives; the circle at their top carries the dome.
sphere radius R = S⁄√2; arches = sphere ∩ side planes (radius S⁄2); ring at h₀ + S⁄2 with radius S⁄2
Place the staircase by three tests: its relation to the principal rooms it serves; keeping the main axial communications free of obstruction; and light, for itself and, as a well of light, for the corridors and vestibules around it.
Cite this page Chris Paton, “Light from a hidden source”, The Textbook of Architecture, https://textbookofarchitecture.com/rule/concealed-light. Text, drawings and models licensed under CC BY-NC 4.0.