How do you read a photometric report?
Reading what was tested, what was measured and whether it meets the requirement, point by point, with the limits of the result.
Photometric report interpretation is reading a laboratory report so that you know what was tested, under what conditions, what was measured and whether it meets the requirement. Start with the identity of the fixture, its source and colour, the rated current, the test distance and the standard used, because a result applies only to that sample and set-up. Then read the intensity data, usually as a table and an isocandela diagram that shows the shape, size and position of the beam.
The key step is to compare the measured values with the requirement point by point: the standard sets minimum, and sometimes maximum, intensities at defined points or areas, and, where a limit is set at a point, one point outside it is a failure however good the rest of the beam looks. Every light with a colour requirement, white included, also has its chromaticity checked against the colour limits. The conclusion is then read with its limits: it describes the tested sample with the laboratory's uncertainty, not every unit made, and not how a fixture is aimed or maintained in service.
Frequently Asked Questions
Q1What is photometric report interpretation?
It is reading a laboratory's photometric report so that you know what was tested, under what conditions, what the measured light output was, and whether it meets the requirement. The report is read against the requirement, not as a set of numbers on its own.
Q2What should I check first in a report?
What was tested and how: the fixture model and configuration, the light source or lamp, the colour, the current it was run at, the test distance, and the laboratory, date and standard used. A result only applies to the sample and set-up described.
Q3How do I compare the data with the requirement?
The standard specifies minimum and sometimes maximum intensities at defined points or inside defined areas of the beam. Each requirement is compared with the measured values at the same angles, in the form the standard states it (some limits are averages over an area, not single points). Where a limit is set at a point, any point outside it is a failure, however good the rest of the pattern looks.
Q4What does an isocandela diagram show in a report?
Lines of equal intensity drawn over horizontal and vertical angle. It shows the shape, size and position of the beam at a glance, and the requirement can be drawn over it as a contour, so any part of the beam that falls short of the required area can be seen.
Q5Is colour part of the report?
Yes, for every light that has a colour requirement, white included. The measured chromaticity is compared with the colour limits in the standard. A light can meet the intensity requirement and still fail on colour, or the reverse, so both are read.
Q6What are the limits of a report's conclusion?
It applies to the tested sample under the stated conditions, with the measurement uncertainty of the laboratory. It does not by itself show that every unit made will perform the same way, or that the fixture is correctly aimed or maintained on the airfield.
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