This document discusses spectrophotometry, including the Beer-Lambert law, instruments used, and applications. Spectrophotometry measures light intensity as a function of wavelength by diffracting light into a spectrum and detecting intensities. Instruments include a light source, monochromator to produce monochromatic light, cuvettes to hold samples, and detectors to convert light to electrical signals. Applications include concentration measurement using standard solutions, detecting impurities, structure elucidation of organic compounds, studying chemical kinetics, and determining functional groups and molecular weights.