Wavelength detection of monochromatic light beams can be achieved with a pair of optical sensors located behind a linear variable filter. The active area of one sensor increases, whereas that of the other sensor decreases along the direction of increasing value of transmission wavelength of the filter. By computing the ratio of the photoresponse of one sensor to the other, the wavelength can be obtained from a calibration chart. Proof‐of‐concept wavelength detectors were constructed using photoresistive superconductor sensors. Results obtained for the spectral range of 700–1100 nm are presented and discussed. ©1996 American Institute of Physics.