What is beam pattern?
The shape a fixture’s light makes around its beam axis: where it is concentrated, and how it tapers toward the edges.
Beam pattern is the shape of a fixture’s beam. Mark every direction by its angle from the beam axis, across and up and down, and join the directions that have the same intensity: the result is a set of nested contours, highest in the middle on the axis and lower in each ring outward. That set of contours is what an isocandela diagram draws.
The pattern is more than one number. Two fixtures can share the same peak candela and still differ in how wide the beam is, how tall it is, whether the peak is centred and how fast the contours close in. AGL patterns are often wider in one plane than the other. Each light type is seen from a different position relative to the fixture, so each has its own required pattern.
Several related entries are parts of this shape. Beam intensity is the values along it, beam spread is its width at a stated level, and beam direction is where its axis points. The pattern is the whole picture they are read from.
Frequently Asked Questions
Q1What is beam pattern in airfield ground lighting?
The shape of a fixture's beam in angle: where the light is concentrated around the beam axis and how it tapers toward the edges. It is drawn as nested contours of equal intensity.
Q2How is a beam pattern shown?
Mostly as an isocandela diagram, with curves joining directions of equal intensity plotted against horizontal and vertical angle. The same pattern can also be given as horizontal and vertical sections, or as a table of candela values at defined angles.
Q3How is beam pattern different from beam spread?
Beam spread is one angle: the width of the beam at a stated fraction of the peak. The beam pattern is the whole shape, including how wide the beam is in each plane, where the peak sits, and how quickly intensity falls away.
Q4Why do AGL fixtures have different beam patterns?
Each type of light is seen from a different position relative to the fixture, so each is built to cover a different region of angles. The pattern required for each light type is set by the standard.
Q5Can two fixtures with the same peak candela have different patterns?
Yes. The peak describes a single point. Two fixtures can share it and still differ in how wide, how tall and how centred the beam is, which is why the pattern is checked against the requirement and not only the peak.
Q6Where does beam pattern data come from?
It is measured during photometric testing and reported by the manufacturer or test laboratory, then compared with the isocandela diagram for that light type in the applicable standard, such as ICAO Annex 14 Vol. I, Appendix 2. Always confirm against the current edition.
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