Beam diameter is the width of a light beam’s base, measured at the point where intensity falls to 50% of its maximum central value.
Beam diameter quantifies how wide a beam spreads at a specific distance, marking the illuminated area where light intensity is half of its peak center value. While beam angle provides an angular measurement, beam diameter translates this into a linear distance, making it a practical metric in lighting layouts. As projection distance increases, small variations in beam angle can greatly affect beam diameter, impacting fixture spacing, overlap, and uniformity. In AV, surveillance, and commercial environments, this measurement ensures lighting delivers the correct balance of focus and coverage.
Beam diameter measurement follows photometric standards defined by the Illuminating Engineering Society (IES) and the International Commission on Illumination (CIE).