Luminosity as a function of time during the early formation phase of the 5 M_♃ planet discussed in Sect. 4. The left panel shows the total luminosity L, the gas accretion shock luminosity L_shock, and the planetesimal accretion luminosity in the sinking approximation L_pla,sink. These luminosities are the ones used in the simulations. The plot also shows the planetesimal accretion luminosity for the cases that the solids would homogeneously mix into the envelope, and if they would stay where they were deposited into the envelope by the impacting planetesimals (no sinking). The right panel shows the same quantities, but normalized to L_pla,sink. Relative to sinking, the heating is reduced by a factor 2 to 3 for mixing, and by a factor 3 to 7 for no sinking.