The Gothic cathedral is, almost definitionally, about light. The light achieved within by the removal of the heavy stonework required by the Roman arch. The light achieved from without by the soaring height enabled by the pointed arch, and the giant glassworks that could be slotted into walls that no longer needed to bear colossal weights. And the light within the worshipper, brought closer to their deity through a sublime sensory experience.
That most Gothic cathedrals are, even with the aid of modern lighting, cavernously gloomy places, somewhat contradicts this. They’re dark because the best part of a millennia of smoke from candles, and humidity, and various kinds of air pollution, have turned their insides black -- which is how we now imagine Gothic cathedrals to “naturally” be. If you take a trip out of Paris to Chartres, which has -- to enormous controversy -- been restored to the bright colours of what the best research suggests was its original state, you’ll see something very different. Our forebears, apparently, knew nothing of minimalism or subtlety; the blank stonework that looks down at us from portals, columns and buttresses was once painted colours we’d find garish.