make (something) visible or bright by shining light on it; light up

a flash of lightning illuminated the house

his face was illuminated by a smile

help to clarify or explain

placing the events of the 1930s in a broader historical context helps to illuminate their significance

decorate (a page or letter in a manuscript) by hand with gold, silver, or coloured designs

this is a carefully written, large-format manuscript illuminated by Leonardo Bellini