  Recently, we introduced a non-perturbative quantization of impulsive
gravitational null initial data. In this note, we investigate an immediate
physical implication of the model. One of the quantum numbers is the total
luminosity carried to infinity. We show that a transition happens when the
luminosity reaches the Planck power $\mathcal{L}_{\mathrm{P}}$. Below
$\mathcal{L}_{\mathrm{P}}$, the spectrum of the radiated power is discrete.
Above the Planck power, the spectrum is continuous and contains caustics that
can spoil the semi-classical interpretation of the resulting quantum states of
geometry.
