A spectrum is a condition that is not limited to a specific set of values but can vary, without steps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colours in visible light after passing through a prism. Related to Normal spectrum: Prismatic spectrum a representation of a spectrum arranged upon conventional plan adopted as a standard, especially a spectrum in which the colures are spaced proportionally to their wavelengths, as when formed by a diffraction grating.
The band of colours obtained on the screen, when a polychromatic light splits into component colours is called a spectrum.
When a light ray enters one refracting surface of the prism, it bends towards the normal, and when it emerges out of the other refracting surface, it bends away from the normal. The angle between the incident ray and the emergent ray is the angle of deviation.
The phenomenon due to which a polychromatic light, like sunlight, splits into its component colours, when passed through a transparent medium like a glass prism, is called dispersion of light.