Tillering in wheat (Triticum aestivum L.) is influenced by both light intensity and the ratio between the intensities of red and far-red light. The relationships between canopy architecture, light properties within the canopy, and tillering in spring-wheat plants were studied using a 3D virtual plantmodelling approach. The advantage of virtual plant models is that each element in the architecture of the canopy is given an explicit 3D representation, which enables simulation of processes at the level of individual organs. The model used, called `ADELwheat¿, was calibrated for spring wheat. The model was validated for ground cover and leaf area index, using an independent dataset. Experimentally, it was shown that new tillers ceased to appear when the fraction of light intercepted by the canopy exceeded 0.4. That threshold was independent of plant population density, shading, developmental stage of the plants and rank number of the tiller. At the time tillering ceased, the red/far-red ratio (R:FR) was fairly similar across population densities. Cessation of tillering in ADELwheat was therefore made dependent on thresholds of light properties. A light model (`nested radiosity¿) was coupled to ADELwheat and was used to calculate both PAR interception and R:FR at the level of the individual organ while employing a series of different thresholds. The simulation results show that the virtual plant-modelling approach is useful to simulate global effects of local stimuli. The study demonstrates that the virtual plant-modelling approach can provide insight into the factors that determine the developmental plasticity of wheat in terms of tillering.