An external cavity semiconductor laser light source comprises includes a semiconductor gain device operable to provide light amplification; a wavelength selection element including a diffraction grating; and light re-directors. The gain device, light re-directors and grating are arranged so that an optical resonator is established for light portions emitted by the gain device and diffracted by the diffraction grating. The resonator is an external cavity laser resonator. The light source is capable of varying an angle of incidence of radiation circulating in the resonator onto wavelength selection element to select a resonator radiation wavelength dependent on the angle of incidence.