Use of a transmission electron microscope to irradiate silicon carbide samples has been demonstrated as a useful additional characterisation technique. The photoluminescence spectra of crystal defects introduced in this way have been found to be extremely rich in detail, involving more than 50 zero phonon lines. It is perhaps disappointing that relatively few of these optical centres have been identified conclusively. Indeed, controversy exists over most of the interpretations that have been advanced. As a step towards clarifying this situation we have been studying many of the more important photoluminescent systems by investigating the dependence of the results on the sample n- and p-doping levels, their stoichiometry, the source of supply, the electron dose, the subsequent annealing history, and by exploiting two new aspects of the technique that will be introduced here. A brief review will be given of new results obtained for some of the major optical centres. Most of the irradiations have been performed at room temperature using 300 kV electrons but some were carried out at 750°C.