Abstract: Lith effect appears only when the induction period conditions are strictly controlled. The conditions required can be achieved with the aid of the corabination of the two actions: development acceleration and development inhibition. The development acceleration caused by semi-quinone shortens the induction period of the grains bearing larger latent-image leading to the narrow distribution of the induction period among grains. The passivation of the development centers lengthens the induction period of the grains bearing smaller latent-image resulting in the dependance between the apparent induction period and exposure. Lith effect appears as the consequence of the different affected degree of the two actions in different exposures.

Key words: development accelaration, development inhibition, Lith effect