1. A method for estimating physical properties of a scene comprising a scene object illuminated by a scene illuminant, said method comprising: a) illuminating said scene with modulated light from an emitter, said modulated light having a predetermined spectral power distribution; b) detecting backscattered light from said scene using a detector; c) analyzing output from said detector to distinguish between illuminant output and emitter output, wherein said illuminant output represents backscattered light from said scene illuminant, and said emitter output represents backscattered light from said emitter; and d) estimating physical properties of said scene object in dependence upon said emitter output and said predetermined spectral power distribution.