An instrument for measurement of color, i.e., for identifying in some unique and standard way the colour of an object. One form, used for opaque objects, compares the object with a set of standard colors. Another, used for light-emitting objects such as lamps and stars, compares the light from the object with light of known composition passed through coloured filters. Yet another, used for translucent substances such as philtres or coloured solutions, passes light of known composition through the substance and determines the amount of light absorbed in various parts of the spectrum. A colorimeter differs from a spectrometer primarily in that it gives the colour of an object (or the light from it) by specifying how that colour can be made up from a small number (from 1 to 3; usually fewer than 9) other, standard colors. A spectrometer gives the colour of the light from an object in terms of the intensity of the light as a more or less continuous function of wavelength.