A new class of models-two-dimensional line source with parallel plane emission, or 2D-LSPP-has been proposed for estimation of photon incidence in annular reactors. These models are similar to the well-known line source with parallel plane emission (LSPP) radial model, but these incorporate the axial distribution of photons at the boundary condition (i.e., at the reactor inner wall), which is a characteristic of the line source with spherical emission (LSSE) model. The new models have the advantage of easy implementation in numerical schemes, because only the radial direction must be considered during the calculations. Photon losses through the upper and lower cross-sectional cores are also automatically taken into account, as a function of the lamp length and the system geometry, which is a desirable model property in scale-up procedures that does not exist in the classical LSPP model. In this work, these new models are derived and simulation results are shown for comparison with the LSSE model. Some advantages of the new models are discussed, as well as their application limits.