This paper presents a test case for coupling two physical aspects of an LED, optical and thermal, using specific simulation models coupled through an open source platform for distributed multi-physics modelling. The glue code for coupling is written with Python programming language including routines to interface specific simulation models. This approach can also be used for any other software. The main optical simulations are performed with an open source ray tracer software and the main thermal simulations are performed with Comsol Multiphysics. We show how to connect a Mie theory based scattering calculator with the ray tracer. Simulation results are compared to measured samples. The total radiant power emitted by the modelled LED is shown to be up to 3% consistent with the measurements.