Spectrum in photography and optics usually refers to the visible portion of the electromagnetic spectrum, which is the range of light detectable by the human eye. It appears as a band of colours produced when white light is separated by diffraction or passed through a prism, splitting into its component wavelengths. These colours are arranged in order of wavelength, typically from violet at the shortest wavelength through to red at the longest.
The visible spectrum is fundamental to photography because it determines how colour is captured, reproduced, and perceived in an image. Understanding the spectrum helps photographers work more effectively with colour temperature, filters, lighting conditions, and white balance settings. It is also important in specialist areas such as infrared and ultraviolet photography, where imaging extends beyond the visible spectrum into wavelengths not normally seen by the human eye.