A numerical model has been developed for the dynamic simulation of heat and radiation transfer from lamps and ballasts in an enclosure. The model, named LITEAC1, calculates temperatures, cooling loads and illuminances at each simulation time step. LITEAC1 is an improvement upon existing models in the literature in the following aspects: it performs dynamic simulation for all nodes without assuming that some nodes are massless; it calculates illuminances on room surfaces; and it runs faster on a desktop computer. In order to refine the simulation of the two-way interaction between lighting and HVAC systems, a fluorescent lamp positive column discharge model, named LAMPPC, has been incorporated into LITEAC1 to improve calculation of the conversion of input electrical energy into light, thermal radiation and heat. LAMPPC employs established principles in plasma physics to quantify the energy conversion processes.