A special form of anisotropic scattering phase function is shown to provide an exact solution of the characteristic equation for radiation transfer at depth within a scattering and absorbing medium. The solution is the Henyey-Greenstein function, the degree of extension of which depends on the albedo for single scattering and on the parameter of the phase function. Good applicability of the formulas obtained for a description of integral parameters of light fields in the seawater depth has been demonstrated.