When did the light-on-the-right convention ascend to dominance? I came upon the following wonderful painting by Sofonisba Anguissola, ‘The first great woman artist of the renaissance,’ of her sisters playing chess (painted 1555). 



The painting is truly sublime. Chess players will notice, however, that the color of the squares on the board is the opposite from what is usually used in modern games, with light on the right, and so it made me wonder about the history of this convention. When did the light-on-the-right convention come into prominence? Has it been long established that way? Is this painting illustrating a different custom at that time, or rather might it be explained by an artist inventing a scene and not aware of the custom?
Sometimes chess textbooks would rotate the board by 90 degrees, under the assumption that the players sat at the left and right of the board:


  The only clear evidence of the use of different sources is supplied by the diagrams. While the great majority are oriented in the way universally followed in modern text-books, a small number in each work are at right angles to the ordinary arrangement. These must have been derived from an MS [manuscript], in which the positions were drawn on the supposition that the players were seated to the right and left of the board.


Source: A History of Chess: The Original 1913 Edition by H.J.R. Murray

Murray unfortunately does not give the origins of 'light on right'.