We present new calculations for the kinematics of photon decay into fermion pairs in vacuum, considering an isotropic Lorentz invariance violation (LV) as described by the Standard-Model Extension (SME). These calculations are applied to the interpretation of prompt photon production in LHC data. The inclusive measurement of prompt photon production at the LHC Run 2, with photon transverse energies reaching 2.5 TeV, leads to a lower bound on the isotropic coefficient, $\tilde{\kappa}_{tr} > -1.06\times 10^{-13}$ at 95% confidence level. This improves the previous collider constraint by a factor of 55. Additionally, the derived kinematics of photon decay can be utilized to further constrain LV coefficients through the detection of fermion pair production, such as top-antitop events.