When it comes to colorimeters, let’s first introduce photometry. Photometry is the general name given to the techniques which use the detection of light radiation and changes in radiation intensity. If the measured light is in the visible range of the electromagnetic spectrum, then the term applied to the analysis is colorimetry. The basis of the technique is that a beam of light from a light source (usually a tungsten lamp) passes through a cuvette or test tube containing the compound in solution, the intensity of light leaving the sample will be less than the light entering the cuvette. The loss of light or absorption is proportional to the concentration of the compound. The color of the sample can be an inherent property of the solution or can be developed by the addition of suitable reagents. The absorption of the sample is compared with that of standards containing known amounts of the sample material thereby enabling the sample concentration to be estimated.

A colorimeter is a device used in colorimetry that measures the absorbance of particular wavelengths of light by a specific solution.[1] It 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. (Beer’s Law: According to Beer’s law, when monochromatic light passes through the colored solution, the amount of light transmitted decreases exponentially with an increase in the concentration of the colored substance.)
Lambert’s Law: According to Lambert’s law, the amount of light transmitted decreases. exponentially with an increase in thickness of the colored solution.
In a colorimeter, a narrow beam of light passed through a filter towards a tube containing the colored solution. Any light that passes through the solution is detected by a photocell and a reading of absorbance is displayed on the meter.
A colorimeter can measure the absorbency of light waves. During color measurement, the change in the intensity of electromagnetic radiation in the visible wavelength region of the spectrum after transmitting or reflecting by an object or solution is measured. Such a measurement can help to find the concentration of substances, since the amount and color of the light absorbed or transmitted depends on the properties of the solution, including the concentration of particles in it. A colorimeter is an instrument that compares the amount of light getting through a solution with the amount that can get through a sample of the pure solvent. A colorimeter contains a photocell that is able to detect the amount of light passing through the solution under investigation. The current produced by the photocell depends on the quantity of light hitting it after passing through the colored solution. The higher the concentration of the colorant in the solution, the higher is the absorption of light; less light passing through the solution means less current created by the photocell. Such as, the ATO caliber 4MM handheld color meter can take three wideband readings along the visible spectrum to obtain a rough estimate of a color sample. Traditionally, the word ‘colorimeter’ is used for a device, having three filters that simulate human vision. Colorimeters can be classified into two types: (1) Visual; (2) Photoelectric.
