The three-parameter model of the submarine light field is here proposed. The model consists of three physical parameters: the scalar irradiance (E0), downwelling vector irradiance (Ez) and average cosine (μ) of the submarine light field. This model is derived from a general exponential decay equation that is valid for all submarine light fields free of horizontal divergence. From the exponential decay equation we derive equations for the calculation of radiant power absorbed in a given depth interval and the radiant power scattered into or out of that interval. Calculations of the radiant power attenuation in an East German lake demonstrate that a nepheloid layer functions as an energy trap.