Seekers that sense radiation in the ultraviolet (UV), visual, and infrared (IR) portions of the electromagnetic spectrum are classed as optical seekers. The radiation is transmitted through the atmosphere from the target. Not all target radiation directed toward the seeker will reach it because of attenuation. Optical radiation is attenuated by the geometrical distance from the source (inverse range squared); by absorption and scattering by the atmosphere; by clouds, haze, rain, and snow, and by other obscurants such as smoke and dust. The amount of attenuation is influenced by the wavelength of the radiation.

For example, there are atmospheric transmission windows (relatively lower attenuation) at wavelengths of 1-3 m, 3-5 m, and 8-12 m in the IR spectral region. IR radiation outside these windows is attenuated so severely by the atmosphere that only these windows are used for IR sensors. The 1-3 m band was used by early IR seekers, which were not cooled. The 3-5 m band is the most applicable to current cooled IR seekers. Little of the radiation from the target exhaust plume is contained in the 8-12 m band; thus this band is less desirable for surface-to-air missiles. The visible spectrum is transmitted through a window from 0.4 to 0.8 m, and an ultraviolet window exists from 0.34 to 0.39m. Some seekers are designed to use more than one optical band to discriminate between targets and decoys.

There are three types of optical seekers based on the different techniques used to process the optical image. These methods are reticle, pseudo-imaging, and imaging.