A method of supplementing a main illuminating light with a supplementary illuminating light from a plurality of solid-state light emitters to illuminate a space according to a target illumination spectrum, the method comprising: determining or receiving a reference illumination spectrum associated with the main illuminating light; determining a spectral deviation between the reference illumination spectrum and the target illumination spectrum; and controlling the plurality of solid-state light emitters to emit a respective plurality of emitter beams forming the supplementary illuminating light and illuminating the space with the main illuminating light, the plurality of emitter beams having a respective plurality of emitter spectra together defining a supplementary illumination spectrum of the supplementary illuminating light, the controlling comprising adjusting the plurality of emitter spectra to match the supplementary illumination spectrum to the spectral deviation and illuminating the space according to the target illumination spectrum, characterized in that: said determining the spectral deviation between the reference illumination spectrum and the target illumination spectrum comprises monitoring the spectral deviation over time for changes, and wherein adjusting the plurality of emitter spectra comprises, upon detection that the spectral deviation has changed, adjusting the plurality of emitter spectra to keep the supplementary illumination spectrum matched to the spectral deviation, said monitoring the spectral deviation comprising performing continuous or intermittent real-time measurements of the reference illumination spectrum, the supplementary illumination spectrum, or both the reference illumination spectrum and the supplementary illumination spectrum. determining or receiving a reference illumination spectrum associated with the main illuminating light; determining a spectral deviation between the reference illumination spectrum and the target illumination spectrum; and controlling the plurality of solid-state light emitters to emit a respective plurality of emitter beams forming the supplementary illuminating light and illuminating the space with the main illuminating light, the plurality of emitter beams having a respective plurality of emitter spectra together defining a supplementary illumination spectrum of the supplementary illuminating light, the controlling comprising adjusting the plurality of emitter spectra to match the supplementary illumination spectrum to the spectral deviation and illuminating the space according to the target illumination spectrum, characterized in that: said determining the spectral deviation between the reference illumination spectrum and the target illumination spectrum comprises monitoring the spectral deviation over time for changes, and wherein adjusting the plurality of emitter spectra comprises, upon detection that the spectral deviation has changed, adjusting the plurality of emitter spectra to keep the supplementary illumination spectrum matched to the spectral deviation, said monitoring the spectral deviation comprising performing continuous or intermittent real-time measurements of the reference illumination spectrum, the supplementary illumination spectrum, or both the reference illumination spectrum and the supplementary illumination spectrum.