We propose the Impact-Triggered Flash Cascade (ITFC) model, a phenomenological framework in which visible light is interpreted as a cascade of flashes emitted by an unobservable background of particles (U-particles) excited through contact with a high-speed driver (P-particle). In this picture, the observable signal is not the P-particle itself but the propagation of the U-cascade. The light constant c is reinterpreted as the critical transfer speed of U, while observable information transfer remains bounded by the effective cascade speed, preserving local relativistic consistency.The model is governed by two phenomenological parameters: an effective transfer length and a local dwell/lag time. From these, we derive an effective propagation law and refractive index that consistently account for rectilinear propagation, reflection and refraction, scattering and turbidity, and diffraction and interference through time-synchronization. An effective-action sketch is also provided to encode nonlocal memory and finite transfer range while reproducing the long-wavelength behavior of the model.The present framework may also be viewed as a quantum-interpreted reformulation of a background-medium picture. Rather than reviving a classical ether in its historical sense, we treat the unobservable background as a set of latent degrees of freedom whose localized excitations and transfer dynamics generate the observable optical signal. The present work is intentionally phenomenological; a detailed microscopic model of U-particles, their interactions, and their relation to standard field theory is deferred to subsequent papers. Possible large-scale background modulation may be explored in future work, but it is not essential to the present quantum-interpreted phenomenology of local light propagation.