4. The critical closure density is 3H²/8.pi.G = 9.2x10^-27 h₇₀² kg m^-3 =1.35x10¹¹ h₇₀² M_sol Mpc^-3. Dividing this by the observed luminosity density (for H₀=70) gives M/L_B=804 solar units for closure.

j_B is proportional to the Hubble constant since luminosities scale as H₀^-2, distances scale as H₀^-1, and hence volumes go as H₀^-3.   Thus the luminosity density scales as H₀.