LIRF is due to inefficiency of forming a latent image, and this reduces photographic speed but increases contrast. Due to low level of exposure irradiance (intensity), a single crystal may have to wait for a significant amount of time between absorbing sufficient number of photons. In the process of making a stable latent image center, a smaller and less stable silver speck is made. Further generation of photoelectrons is necessary to grow this small speck to a larger, stable, latent image. There is a finite probability that this intermediate unstable speck will decompose before next available photoelectrons can stabilize it. This probability increases with decreasing irradiance level.