What is photometric inspection?
The measurement of what the lights actually deliver — intensity, beam and colour at defined points, taken at a steady intensity step and compared with design values and the standard.
Photometric inspection measures the light itself rather than the hardware around it. The sequence is prepared and permitted, fixtures are cleaned and aligned while isolated, the circuit is then set to a defined intensity step and allowed to stabilise, and intensity, beam and colour are measured at defined points and compared with the design values and the standard.
Cleaning first matters: a dirty lens or tilted fixture gives a low reading that says nothing about the optics. Measuring every light at the same, steady step makes the results comparable. Hands-on work is done with the circuit isolated, locked out and proved dead under the airport’s permit-to-work, and measuring is done with the lights on and people and equipment kept clear of the movement area as procedures require.
- Prepare. Obtain the permit and access, collect design values and earlier results, and confirm the photometer is in calibration.
- Clean & align. With the circuit isolated and proved dead, clean lenses, check the lamp or LED source and verify fixture aim.
- Set up. Re-energise, set the circuit to the test intensity step, confirm the CCR output current for that step and allow output to stabilise.
- Measure. Take intensity, beam and colour readings at the defined measurement points.
- Compare. Judge readings against design values, the isocandela diagram, the standard and earlier results.
- Act & log. Clean, replace or realign where needed, re-measure, then record and trend the results.
Frequently Asked Questions
Q1What is photometric inspection in airfield ground lighting?
It is the measurement of what the lights actually deliver: light intensity, beam direction and pattern, colour and uniformity along a row of lights. Readings are taken at defined points with a calibrated photometer and compared with the design values and the applicable standard.
Q2Why clean and align the fixtures before measuring?
Dirty lenses, tilted fixtures and failed lamps or LED modules produce low or distorted readings that are not the true performance of the light. Cleaning and aligning first means a poor result points to a real fault in the optics or source rather than to something simple to correct.
Q3Why is the circuit set to a specific intensity step?
Light output changes with the current step of the constant current regulator. Measuring every light at the same, stable step makes results comparable between fixtures and between inspections. The step used is set by the test procedure for the site.
Q4Is photometric inspection done with the lights on or off?
The measurements are taken with the lights on, so the circuit is not isolated at that point. Cleaning, aiming and any hands-on work happen earlier under isolation. Measurement equipment and personnel must be kept clear of the movement area as the airport's procedures require.
Q5What is compared against what?
Readings are compared with the design or manufacturer values, the isocandela diagram for the fixture type and the standard's minimum requirements, and with earlier results for the same location. Trends in the readings show gradual loss of output before lights fail the requirement.
Q6What limits and intervals apply?
Minimum intensities, colour limits, measurement points and intervals come from the regulator, the applicable standard, the manufacturers' instructions and the airport's maintenance programme. Always use the values for your site rather than a generic figure. As a reference point, ICAO treats a light as unserviceable when its main-beam average intensity falls below 50% of the specified value (or of the higher design value, where a light is designed above it), and its guidance gives minimum in-field measurement frequencies for Category II/III precision approach runways: twice a year for in-pavement lights and once a year for other lights. Your regulator may be stricter.
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