The effects of plant density and light intensity on crop growth and yield of cut chrysanthemum were investigated experimentally and simulated with a generic explanatory crop growth model (HORTISIM). In winter, supplementary light (HPS; 48 µ µ µ µmol m-2 s-1 PAR) increased total incident PAR with 24%, whereas total dry matter production per m 2 was increased with 45%. The effect of supplementary light on plant dry and fresh mass, and number of flowers per plant at different plant densities (32, 48 or 64 m-2), was larger at lower densities. In summer, a linear relationship between cumulative dry mass production and cumulative intercepted PAR was observed in each of three shading treatments. However, the slope of this line (light use efficiency) decreased with increasing light level being 4.1 g MJ-1 , 3.4 g MJ-1 and 2.7 g MJ-1 for 43%, 66% and 100% light, respectively. HORTISIM could accurately predict crop growth and yield at most light conditions, with measured climatic data, initial plant mass and time course of leaf area index being model inputs. However, in summer at 100% light the model strongly overestimated dry mass production.