Photometric data describes a lamp’s measured light performance, including luminous flux, luminous intensity, illuminance, and the spatial light distribution. It may be presented as light-distribution diagrams, isolux plots, intensity tables, or digital photometric files and should include the measurement conditions. This information allows designers to predict and compare how a light performs at defined distances and angles. A lumen value alone cannot show coverage, reach, uniformity, or glare. Reliable comparison requires data for the complete lamp and stated operating conditions, together with consistent units, orientation, coordinate system, and measurement or calculation method.