A spectrophotometer measures the intensity of light transmitted or absorbed by chemical substances. It consists of a light source, monochromator to produce specific wavelengths, sample cell, and detector. There are two main types - single beam measures light intensity before and after a sample, while double beam compares light intensities between a reference and sample path. Spectrophotometers are used across various fields like chemistry, biochemistry, materials science, and more to analyze properties of substances, detect chemical components, and study how compounds interact with light.