A hypothesis explaining the diffraction and interference of light from a pure corpuscular point of view was published in 2018. The author developed the idea by a fortunate combination of intuition and statistics but failed to justify it theoretically. This vagueness can be amended by using relativistic invariants. Adapting Dirac’s equation to gravitational potentials acting over photons yields most of the properties of light. A complete characterization of the properties of light arriving from distant galaxies was performed by modeling the coherence of light. It was assumed that the coherence of light is generated by two orthogonal potentials. Here an idea explains the cosmological redshift data as is done by the combination of Big-Bang, acceleration, and deceleration trilogy.