What characterizes a monochromatic light source?

A monochromatic light source is characterized by emitting light of a single wavelength or color. This means that all the light produced by the source corresponds to one specific wavelength, which results in a uniform color appearance. Monochromatic light is often used in various scientific applications, including spectroscopy and laser technology, because it provides a clear and consistent spectrum that makes it easier to study material properties and interactions without the complications introduced by multiple wavelengths.

The other options highlight characteristics that do not align with a monochromatic light source. For example, emitting light of multiple wavelengths would characterize a polychromatic light source, while emitting light that is invisible to the human eye refers to wavelengths outside the visible spectrum, such as infrared or ultraviolet light. Similarly, emitting light in varying intensities pertains to intensity modulation rather than wavelength, which is not a defining trait of monochromaticity. Understanding these distinctions is crucial in optics, as they can affect how light interacts with matter and how it is utilized in various technologies.