The model corrected for possible distortions in luminosity resulting from non-economic sources like reflections on large bodies of water, which can distort satellite images.
It is similar to a Hertzsprung-Russell (HR) diagram but the latter plots luminosity (or absolute magnitude) rather than just apparent brightness and a knowledge of the distances of the stars plotted is also needed.
Though Dixon wears his eco credentials lightly, his crusade to make low-voltage lighting attractive is second to none, as illustrated by Luminosity, a collection of lamps, lights and shades that he also presented last month in Milan.