Photometry is the science of measuring visible light in terms of its perceived brightness to the human eye. It involves quantifying how much light is emitted, transmitted, or reflected by an object. This measurement is crucial in various fields, including astronomy, photography, and lighting design, where understanding light intensity and distribution is essential for effective applications. The primary unit of measurement in photometry is the lumen, which represents the amount of light produced by a source in a specific direction. Other important units include the lux, which measures illuminance, and the candela, which measures luminous intensity. These measurements help in assessing lighting conditions and ensuring optimal visibility in different environments.