R e is an important length scale in R 4 term in de Vaucouleurs law, which characterizes a specific rate at which surface brightness decreases as a function of radius: I ( R ) = I e ⋅ ⋅ e − − 7.67 ( R / R e 4 − − 1 ) where I e is the surface brightness at R = R e . At R = 0 , I ( R = 0 ) = I e ⋅ ⋅ e 7.67 ≈ ≈ 2000 ⋅ ⋅ I e