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How does stained glass shape the experience of light inside a Gothic cathedral?

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The Great Court at the British Museum in London features a large central rotunda surrounded by wide steps and a glass and steel lattice roof, with visitors walking throughout the space. — Architecture The Great Court, designed by Foster and Partners, 2000; in the British Museum, London.

In the context of Gothic architecture, stained glass acts as a transformative medium that turns natural sunlight into a mystical, supernatural experience. By filtering and coloring light, these windows modify the interior atmosphere, creating a sense of "mystical diffusion" that descends from above.1

The experience of this light is dynamic, shifting throughout the day based on the sun's position, intensity, and atmospheric conditions. For instance, as the sun moves, different windows within a cathedral like Chartres Cathedral come to life, while others recede into a "hushed twilight". This interaction between physical light and the viewer's adaptive vision creates a constantly changing environment.2

Historically, the effect was carefully calibrated:
* Early Gothic: Artisans used deep, saturated colors to create a brilliant, intense contrast against the surrounding darkness of the interior.2
* Rayonnant Style: As architectural techniques allowed for larger windows and thinner walls, the glass became lighter in color to increase visibility and admit more illumination, shifting the aesthetic toward more luminous, less "awesome" effects.23

Ultimately, stained glass functions as a form of "painting with light," where the glass colors, refracts, and fragments the sun's rays to define the cathedral's spiritual and visual character.2