Pageant waggon plays, performed out of doors in high summer, sometimes call, improbably at first sight, for the sudden appearance of a great light, usually emanating from God or Christ. Drawing on a wide range of contemporary evidence, this article explores how, with reflectors, the light of the sun could have been used to produce some dazzling effects, and shows how in the York pageants of the Nativity, the Transfiguration, and the Creation and Fall of the Angels, this light is not only theatrically exciting but thematically significant. The second part will look at the position of the sun at various stages of Corpus Christi Day, which involves a consideration of the time-frame of the whole days’ events.