What is the photometric testing process?
The sequence by which a fixture is measured in the laboratory: prepare, align, stabilise, scan the grid, check, record and report.
The photometric testing process is the sequence by which a fixture's light output is measured in the laboratory so that it can be compared with a requirement. The fixture is prepared and mounted, aligned on the goniometer, and run at its rated current until its output is stable. The photometer then reads the intensity at each point of the measurement grid as the fixture is turned, angle by angle.
The readings are checked by repeating a reference reading during and after the scan, so drift in the output, the alignment or the photometer is caught, and any affected part is repeated. The intensities are recorded as a table, with colour measured too (white lights have colour limits as well as coloured ones), and turned into an isocandela diagram and a photometric report, which is compared with the applicable standard.
Frequently Asked Questions
Q1What is the photometric testing process?
It is the fixed sequence by which a fixture's light output is measured in a laboratory: prepare and mount the fixture, align it, run it at rated current until it settles, scan the measurement grid angle by angle, check and record the readings, and produce a report from the data.
Q2Why must the fixture be stabilised before measuring?
Its output changes while it warms up, so readings taken too early do not represent the fixture in service. It is run at its rated current until the output is steady, and the output is checked again during and after the scan to confirm it has not drifted.
Q3How is the beam measured across all its angles?
The fixture is turned on the goniometer so that the photometer, at a fixed distance, reads the intensity at each point of the measurement grid in turn. The grid covers the horizontal and vertical angles needed to describe the beam, with finer spacing where the intensity changes quickly.
Q4Why are readings checked during the test?
A repeat reading at a reference angle shows whether the output, the alignment or the photometer has drifted during the scan. If it has, the readings are suspect and the affected part of the test is repeated rather than reported.
Q5What does the test produce?
A table of intensity at each angle, which is turned into an isocandela diagram and a photometric report. Colour is measured as well, because white lights have chromaticity limits just as coloured ones do. The report is then compared with the requirement in the applicable standard.
Q6Who decides the test conditions and limits?
The applicable standard and the test laboratory's procedure set the grid, distance, current, tolerances and acceptance limits. The sequence here is the common pattern, and the details are not set by this entry.
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