Whilst all phases of Gothic architecture were concerned to some degree with levels of illumination and the appearance of structural lightness, Rayonnant takes this to the extreme.
As well as increasing the size of window openings, the Rayonnant period coincided with the development of the band window, in which a central strip of richly coloured stained glass is positioned between upper and lower bands of clear or grisaille glass, which allowed even more light to flood in.