A colorimeter is an instrument that determines the concentration of an aqueous solution by measuring the light absorbed by a sample that has been mixed with a colorimetry reagent. It has a chamber for holding a sample, and a light source, usually an LED, which projects a specific wavelength of light onto the sample. Light that passes through the sample is recorded by the colorimeter's light detector and compared to a reference standard, providing a color measurement based on the intensity of sample's color. Although it is sometimes called a color spectrometer, a colorimeter usually measures red, blue, or green wavelengths rather than any wavelength of visible light. Colorimeters are commonly used for water quality analysis in manufacturing, mining, and water treatment plants, and for color analysis in photography, printing, and other industries.
Most colorimeters have an LCD that shows readings and are single-parameter testers that are calibrated for a particular substance such as calcium, chlorine, chromium, fluoride, iron, iodine, manganese, nitrate, ozone, phosphate, or sulfate. A multi-parameter colorimeter can generate a range of wavelengths and may test for multiple properties. Colorimeters may be either battery-operated, handheld units for field testing, or electric-powered, benchtop units for laboratory and industrial testing. Among the factors to consider when selecting a colorimeter are the testing range, resolution, and accuracy. Other features may include a backlit display, data logging capability, an output for connecting to a computer, and automatic shutdown to preserve power. Certain models are Ingress Protection (IP) rated against dust and water.
The most common units of measurement for a colorimeter are parts per million (ppm) or parts per billion (ppb) for measuring the concentration of a solute, and platinum-cobalt units (pcu) for measuring water color. A colorimeter is often used with a cuvette, a rectangular or cylindrical container for holding samples undergoing optical analysis. Some kits include a colorimeter and accessories such as reagents, cuvettes, and syringes.