Decarbonisation of the energy systems is critically required to meet the global obligations set out in the Paris Climate Change Agreement. An evaporative cooling system, by using the latent heat of water cycling in the atmosphere, can cool air without the use of significant electrical and thermal energy. However, its cooling capacity is limited by the moisture content of the intake air. To achieve near-zero-carbon air-conditioning operation at any climate condition, the combination between an evaporative air cooling (e.g. dew point air cooling) and a renewable-driven air dehumidification is clearly a promising solution. A novel light-driven air dehumidification system using a photo-thermal material which can absorb solar light energy to excite photo-induced drying process is under investigation by authors, in the meantime, a novel solar tube system which can collect, concentrate and transmit solar light for application in the light-driven air dehumidification system is studied. This paper introduces the novel light-driven air dehumidification system and its driven source, i.e., solar tube system, and presents computer simulation work for study on light transmission performance in the solar tube system. Computer model for light transmission performance simulation on both straight and bend solar tubes has been developed and validated. Simulation work has been carried out for various geometries and light incidence angles. The results are analysed and discussed.