How is a beam measured?
Scanning intensity across angle to find where the beam points, how strong it is and how wide it spreads.
One intensity reading describes one direction. Beam measurement repeats it at many angles, turning the fixture step by step in front of the photometer, so the readings trace the shape of the beam.
Three results come from the scan: the peak and the beam axis where it occurs, and the beam spread, the angular width between the points where intensity falls to a stated fraction of the peak. The scan is made in the horizontal and vertical planes, and the beam axis is compared with the fixture’s reference axis to check its aim.
Frequently Asked Questions
Q1What is beam measurement?
Measuring how a fixture's light is spread across angle. The fixture is scanned in front of a photometer to find where the beam is strongest, how wide it is and how its intensity falls away at the edges.
Q2How is beam measurement different from light-intensity measurement?
Intensity measurement gives the candela value in one direction. Beam measurement repeats that at many angles, so the result describes the shape, width and aim of the whole beam.
Q3What is the beam axis?
The direction of peak intensity found during the scan. It is compared with the fixture's reference axis to show whether the beam is aimed where it should be.
Q4What is beam spread?
The angular width of the beam between the two points where intensity falls to a stated fraction of the peak. The fraction is set by the applicable standard or the manufacturer's data.
Q5Why is the beam measured in two planes?
A beam is rarely the same width in every direction. Horizontal and vertical scans through the peak show the spread and aim in each plane, which matters for fixtures seen from a set approach direction.
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