Improvements in and relating to spectral sensing

Target object 54 is illuminated with optical radiation from multiple spectrally distinct light sources 52a etc. Information identifying each light source distinguishably from the others is respectively encoded by a time-varying intensity modulation. Optical sensor 58 receives reflected components of radiation from each of the sources. The encoded information within each component is decoded and an optical spectral band is assigned. An optical reflection spectrum is generated from the reflected components according to the respective assigned spectral bands. Reflected components from each source may be measured in separate respective time periods. Encoding may be according to mutually orthogonal pseudo-random codes, performed simultaneously during a common time period. Modulation may be at a rate that is imperceptible to the human eye. The sensor may be a pixel array on which an image of the object is formed. A reflection spectrum may be associated with each image pixel to provide a multi-band or hyper-spectral image. The sensor may be monochrome.