A method of selective light detection uses an optical multi-stable device selectively exhibiting a variety of optical multi-stable characteristics for incident light wavelengths or intensities. The device includes an optically serial connection of two optical bistable elements. Each of the optical bistable elements includes a photodiode having a light absorbing layer including a quantum well structure. The photodiodes are reverse biased by respective voltage sources through respective series resistors so that an optical bistable characteristic for incident light wavelength or intensity is achieved for each photodiode. The characteristic of the second photodiode includes four stable photocurrents at respective wavelengths.