The altarpiece measures 375 × 260 cm when the shutters are closed. The upper panels contain lunettes showing prophets and Sibyls looking down on the annunciation; the lower tier shows the donors on the far left and right panels flanked by saints. The exterior panels are executed with relative sparseness in comparison to the often fantastical colour and abundance of the interior scenes. Their settings are earthly, pared down and relatively simple. Yet there is the same striking use of illusionism which also characterises the inner panels; this is especially true of the faux stone grisaille statues of the saints. Lighting is used to great effect to create the impression of depth; van Eyck handles the fall of light and casting of shadow to make the viewer feel as if the pictorial space is influenced or lit by light entering from the chapel in which he stands.