We have derived an analytical solution for an incoherent component of light scattered by a normally illuminated monolayer of homogeneous spherical particles. It is based on the quasi-crystalline approximation of the theory of multiple scattering of waves as well as on the multipole expansion of electromagnetic fields and tensor Green's function in terms of vector spherical wave functions. We apply the solution to a description of scattering and absorption characteristics of partially ordered monolayers and monolayers with imperfect lattices. The impact of particle size and type of particle spatial order on light absorption is studied. The comparison of calculated and available experimental data is made on the angular and spectral position of the first diffraction order peak for a monolayer with an imperfect triangular lattice from silicon dioxide particles. The theoretical and experimental data are in close agreement.