How is photometric data interpreted?
Turning a table of intensity readings into contours and a peak, then comparing them with the required region.
A table of candela readings is only raw data. Photometric data interpretation turns it into a picture of the beam: the peak and where it falls, the contours that join points of equal intensity, and the way intensity falls away from the centre. Angles are read from the light's reference axis, so the picture only holds at the aiming angle the requirement assumes.
The result is then compared with the required intensity region for that type of light. Many ICAO-based figures define a main-beam rectangle, with a minimum and an average intensity, and a larger outer rectangle with a lower minimum. The question is whether the measured values meet the minimum wherever the standard demands it, and, where it sets a main-beam average, whether the average over the grid points meets that too, and whether the colour and alignment results support the same conclusion. Reading the data this way shows where a fixture falls short, not just that it does.
Frequently Asked Questions
Q1What is photometric data interpretation?
Reading a table of intensity measurements as a picture of the beam. It finds the peak, draws contours of equal intensity and compares the result with the required intensity region.
Q2What is an intensity contour?
A line joining points of equal intensity on the angle-against-angle plot. Nested contours show how intensity falls away from the peak, much like height lines on a map.
Q3What does the required region mean?
The part of the angle plot where the standard sets a minimum intensity for that type of light. The measured values should meet or exceed that minimum at the points the standard specifies, and any main-beam average requirement should be met too.
Q4Why look at the pattern and not only the peak?
A fixture can have a high peak and still fall short elsewhere in the required region. The pattern shows where, which helps find whether the cause is aim, optics or the light source.
Q5How is interpretation different from acceptance?
Interpretation reads what the data shows. Acceptance is the decision, made against the standard's criteria, on whether the fixture is passed.
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