This article needs additional citations for verification. (May 2010) (Learn how and when to remove this template message)
A colorimeter is a device used in colorimetry. In scientific fields the word generally refers to the device that measures the absorbance of particular wavelengths of light by a specific solution. This device is commonly used to determine the concentration of a known solute in a given solution by the application of the Beer-Lambert law, which states that the concentration of a solute is proportional to the absorbance.
The essential parts of a colorimeter are:
- a light source (often an ordinary low-voltage filament lamp);
- an adjustable aperture;
- a set of colored filters;
- a cuvette to hold the working solution;
- a detector (usually a photoresistor) to measure the transmitted light;
- a meter to display the output from the detector.
In addition, there may be:
- a voltage regulator, to protect the instrument from fluctuations in mains voltage;
- a second light path, cuvette and detector. This enables comparison between the working solution and a "blank", consisting of pure solvent, to improve accuracy.
Filters:- Changeable [Filter (optics)|optics filters]are used in the colorimeter to select the wavelength which the solute absorbs the most, in order to maximize accuracy. The usual wavelength range is from 400 to 700 [nanometer] (nm). If it is necessary to operate in the [ultraviolet]range then some modifications to the colorimeter are needed. In modern colorimeters the filament lamp and filters may be replaced by several (light-emitting diode)of different colors.The Measurement of Colour.
In a manual colorimeter the cuvettes are inserted and removed by hand. An automated colorimeter (as used in an AutoAnalyzer) is fitted with a flowcell through which solution flows continuously.
The output from a colorimeter may be displayed by an analogue or digital meter and may be shown as transmittance (a linear scale from 0-100%) or as absorbance (a logarithmic scale from zero to infinity). The useful range of the absorbance scale is from 0-2 but it is desirable to keep within the range 0-1 because, above 1, the results become unreliable due to scattering of light.
- Nuffield Advanced Chemistry (2003)
-  Anzalone GC, Glover AG, Pearce JM. Open-Source Colorimeter. Sensors (2013); 13(4):5338-5346
- The Nuffield Foundation 2003. March 30, 2003. 
- "Colour." Encyclopædia Britannica. Encyclopædia Britannica Online. Encyclopædia Britannica Inc. (2011) Accessed 17 November 2011. 
- "Colorimetry" Encyclopædia Britannica. Encyclopædia Britannica Online. Encyclopædia Britannica Inc. (2011) 17 November 2011. 
- Orion Colorimetry Theory. The Technical Edge. 
|Wikimedia Commons has media related to Colorimeters.|