The decisive value for the brightness of an LED light source is the luminous flux. This describes the actual light output of the light source and is specified in the unit lumen. Luminous flux indicates how much light or brightness a light source emits in all directions. This efficiency describes the ratio of emitted luminous flux in lumens and supplied energy in watts. However, this only provides information about the power that is emitted by the lamp of the spotlight, for example, but not how much finally arrives at a certain surface such as a screen or delimited wall.
ANSI (American National Standards Institute) lumens indicate the brightness produced by a light source and are determined using a standardized measurement procedure. The ANSI lumen is considered a colloquial term in connection with projectors and beamers and plays a major role here, as it describes how brightly, for example, a video projector projects its images onto the wall. The higher the number, at a constant distance from the surface, the brighter the image appears.