Ray tracing is a technique used in geometric optics for calculating the light distribution at the target of an optical system. Monte Carlo (MC) ray tracing is very common in non-imaging optics. We propose a new ray tracing method that employs the phase space of the source and the target of the system. The new method gives a more accurate target distribution than classical MC ray tracing and requires less computational time. It is tested for two-dimensional optical systems. The results for the paraboloid reflector are provided.