Definition of: spectrum

(spek′trəm) noun plural ·tra (-trə)
1. The continuously varying band of color observed when a beam of white light is passed through a prism which separates each component of the light according to frequencies ranging from low for red to high for violet: also visible spectrum, chromatic spectrum.
2. An image formed by radiant energy directed through a spectroscope and brought to a focus in which each wavelength corresponds to a specific band or line in a progressive series characteristic of the emitting source.
3. An after–image. [<L, a vision]