The half-light radius (also known as effective radius ; R e) is a measure that is based on the galaxy's overall brightness flux. This is the radius upon which half, or 50%, of the total brightness flux of the galaxy was emitted. This was first proposed by Gérard de Vaucouleurs in 1948. The choice of using 50% was arbitrary, but proved to be useful in further works by R. A. Fish in 1963, where he established a luminosity concentration law that relates the brightnesses of elliptical galaxies and their respective R e, and by José Luis Sérsic in 1968 that defined a mass-radius relation in galaxies.