Spectrum

The phenomenon that occurs when objects with different spectral power distributions display colours that seem to match. The main reason for metamerism is that colours are sensations, not properties of an object.

A person's eyes can register one and the same sensation from an infinite variety of combinations of different light frequencies. But computer systems need a much larger number of colours to process than human beings, since the human eye is more sensitive to any changes in some parts of the spectrum, while computers distribute the steps evenly across the whole colour spectrum.

Especially when trying to match colours of a photo on the screen to a print of the image, it's important to remember that you can only match colours in a given light.  Something that matches in incandescent light may not match in fluorescent light.

Part of the spectrum that has a wavelength below 390nm.

A light source that contains a mixture of all wavelengths of the visible spectrum.

Black & white film that is sensitive to all colours of the visible spectrum.