In lighting terminology, what does the term “lumen” refer to?

The term "lumen" refers to a measure of light power, specifically the total amount of visible light emitted by a source per unit of time. It quantifies the brightness of a light source as perceived by the human eye and is fundamental in determining how well a lighting fixture will illuminate a space. Understanding lumens is essential for selecting appropriate lighting to achieve desired illumination levels in various environments, whether for residential or commercial applications.

While other options such as a type of lighting fixture, the color temperature of light, or the physical size of a light bulb are all relevant aspects of lighting design, they do not define the measurement of light itself, which is the primary focus of lumens.