Light activation of lead-halide perovskites induces polaronic lattice distortions, here quantified with atomic-level precision. Electron–phonon coupling drives the crystal changes, which are unlocked upon charge-carrier recombination and in the absence of thermal effects. This study clarifies the structure–property relationships in out-of-equilibrium conditions, underpinning the developments of perovskite-based devices. Image credit: Balázs Őrley.