Factors which determine the efficiency of latent image formation in silver halide emulsion grains are discussed in this paper. It is shown that initial photochemical sensitivity to wavelengths of the photographic spectrum between 400 and 1, 200 nm depends on the presence of donor levels introduced by chemical sensitization. Reasons for the ineffective utilization of the absorbed energy are then discussed including desensitization with increasing dye coverage, fluorescence emission from dye layers, and the formation of isolated Ag atoms which do not contribute to the growth of clusters during exposure. The efficiency of latent image formation is increased when a positively charged concentration speck which introduces an acceptor level and provides a radial focusing field for conduction electrons is formed at an early stage of exposure. The quantitative theory of the operation of the concentration speck is presented, and it is shown that the photochemical efficiency is optimized for a thin circular or hexagonal tabular grain forming a central concentration speck and having a radius equal to the drift range of electrons in the field of a unit positive charge.