The optical elements that can combine memory and signal modulation have become a topic of interest in the field of neuromorphic computing systems. In particular, the optical analogue of a memristor called memlumor exhibits promising features in which the change of the output luminescence depends not only on the excitation light signal but also on the state of the material. Metal halide perovskite luminophores are considered to be suitable for memlumor implementation as they exhibit modulation of photoluminescence due to the interaction of structure defects with the environment and previous interactions, thereby possessing memory. Luminescence in perovskite materials is described via Shockley–Reed–Hall model which takes into account charge carriers dynamics in the structure. Additionally, the diffusion of charge carriers also plays a key role and highly depends on memlumor’s size. This paper explores the perovskite memlumor’s functionality based on their characteristic size to identify optimal parameters and suitable designs for future optical neuromorphic computing architectures.