In this work, we model the observed evolution in comoving number density of Lyman α blobs (LABs) as a function of redshift. Our model calculates LAB emission both from cooling radiation from the intergalactic gas accreting on to galaxies and from star formation (SF). We have used a dark matter (DM) cosmological simulation to which we applied empirical recipes for Ly α emission produced by cooling radiation and SF in every halo. Unlike previous work, the simulated volume in the DM simulation is large enough to produce an average LAB number density. For a range of redshifts, z ∼ 1–7, we compare our results with the observed luminosity functions of LABs and Lyman α emitters. Our cooling radiation luminosities appear to be too small to explain LAB luminosities at all redshifts. In contrast, for SF we obtained a good agreement with observed luminosity functions at all redshifts studied. We also discuss uncertainties that could influence the results obtained.