A radiotherapy system comprising a source of radiation, for generating a beam of therapeutic radiation a field light, for generating a beam of optical light that emulates the beam of therapeutic radiation and a collimating device, for collimating the beam of therapeutic radiation and the beam of optical light. The field light comprises a single light-emitting diode (LED) having a single die, and wherein the radiotherapy system does not comprise any lenses outside the LED through which the beam of optical light passes.
