What is a photometric grid?
The set of angular points at which intensity is read, so a whole beam is described by a table of values.
A beam cannot be described by one reading. The photometric grid is the set of angular points, laid out in horizontal and vertical angle, at which the intensity of a fixture is measured.
The grid is centred on the beam axis and extends past the edge of the beam. Every point is read at the same fixed distance and the same set current, so the readings can be compared. At each point the photometer gives one candela value, and together the values form a table of readings from which the beam's shape, spread and compliance are worked out. A finer grid step captures more detail but takes more readings.
Frequently Asked Questions
Q1What is a photometric grid?
The set of angular points, in horizontal and vertical angle, at which a fixture's intensity is measured. Each point gives one reading, and the readings together describe the whole beam.
Q2Why is a grid needed?
One reading gives the intensity in one direction only. A grid samples the beam across many directions so its shape, spread and edges can be worked out.
Q3Where is the grid centred?
On the beam axis, the direction of peak intensity or the fixture's reference axis as the procedure requires, so that readings fall evenly around it.
Q4What is the grid step?
The angular spacing between neighbouring points. A finer step captures more detail but needs more readings, so it is chosen by the standard or the test procedure.
Q5How far does the grid extend?
Far enough to cover the beam and reach past its edges, where intensity has fallen away. The extent is set by the standard or the manufacturer's data.
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