Intermittency effect was studied by use of a multi-flash method where a fixed number of flashes with selected periodic time ( Δt ) were given to model emulsions. The lif etime of a single photon product (latent pre-image) was observed only when the number of flashes exceeded a certain minimum which could be correlated to the minimum size of developable latent image speck. The minimum size was estimated as Ag4. This lifetime and corresponding activation energy, which were strongly dependent on environment, were analyzed on a assumption that O₂^- is the intermediate species for final electron loss.(The observed lifetime at 20°C was 1.1 sec for wet air environment, 16.5 sec for dry air environment and 300 sec for vacuum environment) When the number of flashes was less than the minimum, lifetimes other than that of a single photon product and with somewhat anomalous features were observed; these were discussed in terms of rehalogenation of dispersed latent sub-image specks.