nearmonochromatic

Nearmonochromatic is an adjective used in color science and optics to describe light or colors whose spectral content is very close to a single wavelength. A nearmonochromatic source has a narrow spectral bandwidth centered on a specific wavelength, producing a color with high hue purity but not perfectly monochromatic.

In practice, nearmonochromatic light is produced by sources such as lasers (which are nearly monochromatic but may exhibit finite linewidth), narrowband LEDs, or filtered broadband sources. The spectral power distribution shows a sharp peak; the width is commonly quantified by the full width at half maximum (FWHM), typically from a few nanometers to a few tens of nanometers.

The term contrasts with truly monochromatic light, which would be an ideal single-wavelength line, and with broad-spectrum or polychromatic light, which contains many wavelengths. Near-monochromatic light can be highly sensitive to the observer's spectral response and the illumination, and it may exhibit metamerism with different light sources.

Applications include calibration of optical instruments, colorimetric standards, display technology backlighting, scientific imaging, and art or stage lighting where a precise hue and high saturation are desirable. Limitations include color shifts under varying illuminants and challenges in reproducing exact hues across devices.

See also: monochromatic, narrowband, spectral bandwidth, metamerism.