The tip of a scanning tunnelling microscope can inject hot electrons into a surface with atomic precision. Their subsequent dynamics and eventual decay can result in atomic manipulation of an adsorbed molecule, or in light emission from the surface. Here, we combine the results of these two near identical experimental techniques for the system of toluene molecules chemisorbed on the Si(111)−7 × 7 surface at room temperature. The radial dependence of molecular desorption away from the tip injection site conforms to a two-step ballistic-diffusive transport of the injected hot electrons across the surface, with a threshold bias voltage of +2.0 V. We find the same threshold voltage of +2.0 V for light emission from the bare Si(111)−7 × 7 surface. Comparing these results with previous published spectra we propose that both the manipulation (here, desorption or diffusion) and the light emission follow the same hot electron dynamics, only differing in the outcome of the final relaxation step which may result in either molecular displacement, or photon emission.