What is optical deterioration?
Lenses, reflectors, filters, lamps and sign faces that have lost light output, colour or beam control with age — and how an inspector tells it from dirt.
Optical deterioration means the parts that make, shape or colour the light are losing their performance over time. A lens clouds, yellows or crazes, a reflector coating tarnishes or flakes, a colour filter fades or shifts, a lamp blackens or an LED module dims or loses elements, and a sign face fades or glows unevenly.
Optical deterioration is a change in the part, not a layer on it, so cleaning does not restore the output. A slight change with acceptable output and colour is recorded and monitored. Output or colour falling towards the limit, or visibly crazed or scratched optics, is replaced and re-checked. Output below the minimum, colour out of range or a distorted beam is critical: it is reported and replaced, because pilots rely on the intensity, colour and pattern of the lights.
A change in the lens, reflector, filter, light source or sign face itself. Cleaning does not bring the light back, and the part is replaced.
Dust, film or rubber deposits on the surface. Cleaning as the manufacturer specifies restores the light, so it is cleaned first and the result is judged after.
- Make the area safe. Work under the permit-to-work, with the circuit isolated where the procedure requires it, and allow hot parts to cool.
- Record as found. Photographs before cleaning, with date and location, so any change can be compared next cycle.
- Clean as specified. Use the manufacturer's method and materials; harsh cleaning can itself damage a lens or filter.
- Inspect the optics. Clouding, yellowing, crazing, scratches, tarnish, faded colour, dead LED elements, a faded sign face.
- Check output and colour. Measure with the method in the procedure rather than judging by eye alone.
- Classify and act. Minor, major or critical, then record, replace and re-check, or report and replace, and fix the cause such as water ingress.
Frequently Asked Questions
Q1What does optical deterioration mean in AGL inspection?
A gradual loss of the light output, colour or beam control of the optical parts of a light or sign, such as the lens, reflector, colour filter, lamp or LED, and sign face. It shows as clouding, yellowing, crazing, scratching, fading, dimming or dead LED elements. It is recorded, classified by how far it has gone and what it affects, and acted on according to the site's procedures.
Q2How is optical deterioration different from dirt?
Dirt, rubber deposits and film sit on the surface and cleaning restores the light. Optical deterioration is a change in the material or the light source, so cleaning does not bring the output back. Inspectors clean as the manufacturer specifies first, then judge what is left.
Q3What causes optical parts to deteriorate?
Age, ultraviolet light, heat, abrasion from sand, jet blast and snow clearance, harsh cleaning, chemicals, moisture and water ingress, and lamp or LED ageing. Finding the cause matters, or the replacement part ages the same way.
Q4What does optical deterioration look like?
Clouded or yellowed lenses, crazed or pitted surfaces, tarnished or flaking reflector coatings, faded or shifted filter colour, blackened lamps, LED modules with reduced output or dead elements, and faded or uneven sign faces. A light can look fine by day and still be well below its required output.
Q5How is optical deterioration classified?
By how far it has gone and what it affects. Minor means slight change with output and colour still acceptable, which is recorded and monitored. Major means output or colour is falling towards the limit or the surface is visibly crazed or scratched, so the part is replaced and re-checked. Critical means output below the minimum, colour shifted out of its required range or a distorted beam, and it is reported and replaced. The limits and exact grading come from the manufacturer, the project specification and the site's inspection procedure.
Q6Why does it matter to pilots?
Pilots rely on the intensity, colour and pattern of airfield lights to see and understand the layout. Dim, off-colour or distorted lights give weaker or wrong cues, and guidance systems such as PAPI depend on correct colour and beam control. Light output is measured with the method in the procedure, not judged by eye alone.
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