The present invention provides a light source for producing a substantially balanced output at a substantially optimised output intensity. In one embodiment, the light source comprises one or more light-emitting clusters of a first type and one or more light-emitting clusters of one or more other types, each one of which comprising one or more light-emitting elements, such that, when all light-emitting elements are driven to provide a substantially optimised output intensity, the spectral output of the one or more light-emitting clusters of the first type is substantially balanced by the spectral output of the one or more other light-emitting clusters.