beamangle

Beam angle is the angular width of a light source’s emitted beam, typically defined as the angle between the directions on either side of the central axis where the luminous intensity falls to 50% of its maximum. It describes how widely the light spreads from the source and is a common descriptor for LEDs, flashlights, stage lighting, and automotive headlights. A small beam angle yields a narrow, concentrated beam with higher on-axis intensity, while a large beam angle produces a broader, more diffuse illumination.

In practice, beam angle is determined from measurements of the light’s luminous intensity distribution, usually with a goniophotometer. The angle is found from the polar distribution by identifying the directions where intensity equals 50% of the peak and measuring the separation between them. Some manufacturers and standards use alternative thresholds (for example 10% of maximum or full width at half maximum), so the term can vary in exact definition across products and contexts.

Beam angle should be understood in relation to other photometric properties. It is not a measure of total light output, efficiency, or color quality; rather, it characterizes the spread of light around the main beam. The optical design elements—such as lenses, diffusers, and reflectors—and the source geometry largely determine the beam angle. In lighting design, beam angle interacts with distance and the size of the illuminated area to influence coverage, glare, and uniformity.