Two designs of wavelength detector intended for field applications are presented. The first design makes use of a pair of 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. The second design involves the use of a pair of identical sensors, one of which is coated with a spectrally variable attenuator. For both designs, by computing the ratio of the photoresponse of one sensor to the other, the wavelength of monochromatic light is obtained from a calibration chart. Experimental wavelength detectors were constructed using superconductor and semiconductor dual sensors. The results obtained in the spectral range of 0.6 - 7 micrometer showed that sensitive, accurate detection of wavelength can be achieved for a wide range of incident angles.