Introduction
Spectrophotometry is a technique that measures how much a substance absorbs light by measuring the intensity of light, as a beam of light passes through it. The basic principle is that every compound absorbs or transmits light over a certain range of frequencies (wavelengths). If we take a measure of this, it could be used to measure the amount of a known substance in an unknown medium. Spectrophotometry is one of the most useful methods of quantitative analysis in various fields such as chemistry, physics, biochemistry, forensic science, agriculture, material and chemical engineering and clinical applications. A spectrometer gives the detail of exactly which all wavelengths of light are absorbed and which all wavelengths of light are reflected, whereas a colorimeter gives a comparative measure by measuring the relative intensity of the light absorbed or reflected at a particular wavelength of light. Spectrometric and spectrophotometric techniques can be used for a wide range of elemental and compositional analyses that provide very high and accurate detection limits in the sub-ppm level of chemical compounds which could be made useful in various applications. Some of the colorimeters can be used to monitor the separations obtained while doing liquid chromatography and some others could be used for color selection and printing. The optimum balance of NPK in soil and protein concentration in various substances can also be monitored by the use of spectrometers. Thus there are many key areas where spectrometry and spectrophotometry are used like pharmacology, industries, agriculture, printing, painting.

Applications
In Pharmacological Laboratories
In laboratories, UV and colorimeters can be used to monitor the separations obtained while doing liquid chromatography. If a mixture is separated into columns, colorimeters can be used to detect the different compounds. Using a colorimeter is relatively cheap and an easy detector method compared to mass spectrometry detectors. Many illegal drugs contain aromatic groups that produce characteristic UV/Visible spectra. As the absorption peak depends on the nature of the aromatic group(s) in the drug compound, additional spectroscopic information regarding drug derivatives and their metabolites will be obtained.
In Digital printing
Colorimeters are widely used in digital printing techniques for color selection and confirmation. A spectral reflectance curve is obtained by taking the readings at every 10 nm along the visible wavelengths (400 – 700nm). These curves confirm a particular color to a given specification. The color management process requires a reference color data set and software for analyzing the measured data in addition to a colorimeter.
In Agriculture
In the field of agriculture, production of the crop, water, nutrition management, etc. are directly knotted with maintaining the optimum balance of nitrogen, phosphorus, and potassium in the soil for the specific crop concerns. The correct nutrient levels together with correct soil pH levels also support nutrient availability, organic matter decomposition, and overall soil fertility balance. A caliber 8mm portable colorimeter acts as an important tool for monitoring the nitrogen and phosphorus levels in fertilizers and soil compounds.
Estimation of protein concentration
Due to the presence of tyrosine and tryptophan, the proteins absorb UV light at a maximum wavelength of 280 nm. The tyrosine and tryptophan content varies with different proteins and hence the absorption peak. The absorption peak at 280 nm is hence used as a rapid and very sensitive measure of protein concentration. Even though we could obtain accurate readings from a spectrometer/ colorimeter, there are some common limitations. Dust or grim coated over the mirrors in a double-beam UV-Visible spectrometer may degrade the device’s performance. Also, the stray light caused by faulty equipment design could decrease an instrument’s linearity range and reduce the absorbency of the substance it measures. Another factor is that the electronic components in the spectrometer or sample source may generate noise that decreases measurement accuracy and reduce the device sensitivity.

Conclusion
A spectrophotometer is a measurement of how much a substance absorbs or transmits light, which is widely used for quantitative analysis in various areas of science and engineering. Any application that deals with substances or materials can use this technique for quantitative as well as qualitative analysis in biochemistry. Colorimeters offer very high accuracy and lend a helping hand in eliminating human error with high-speed wavelength scanning of samples across the UV and Visible spectrum.