What is optical efficiency?
How much of the light a source produces actually leaves the fixture, once the lens, reflector and filter have taken their share.
Optical efficiency is the share of the light a source produces that actually leaves the fixture. It is the flux out divided by the flux in, so it is always less than one: every lens, reflector and filter takes a little of the light on its way through.
The losses come from absorption and scattering in the optical parts. A colour filter is usually the largest single loss, because it makes colour by blocking the rest of the spectrum, while a source that already emits the right colour needs less filtering. Dirt on the lens and ageing of the materials lower efficiency further in service. Optical efficiency covers the light path only and is separate from the electrical efficiency of the driver or power supply and from the luminous efficacy of the source itself, which is its lumens per watt. What the fixture must deliver at the end is still set by its intensity in each direction and its colour.
Frequently Asked Questions
Q1What is optical efficiency?
The fraction of the light produced by the source that actually leaves the fixture. It is the output flux divided by the flux of the source, so it is always below one.
Q2Where is light lost inside a fixture?
In the optical parts. A lens and a reflector absorb and scatter a little, and a colour filter absorbs a large share of the light it does not pass. Dirt and ageing add further losses over time.
Q3Why do coloured lights lose more?
A filter makes colour by blocking the rest of the spectrum, so the light it removes is lost. A source that already emits the colour needs little or no filtering and wastes less.
Q4Is optical efficiency the same as the efficiency of the whole fixture?
No. Optical efficiency covers the light path only. The electrical efficiency of a power supply or driver is a separate matter, and the overall result depends on both.
Q5Why does optical efficiency matter in AGL?
The fixture must still deliver the required intensity in each direction and the correct colour. Higher optical efficiency means less source power is needed for the same output, and cleanliness keeps it from falling in service.
See It. Understand It. Then Learn How to Engineer It.
Recognising an AGL system visually is the first step. The next step is knowing how to design, install, test, commission and maintain them correctly.
Build Practical AGL Engineering Skills
Go deeper with structured training from Precision AGL Academy, covering:
Learn how each light, sign and circuit works as part of a complete airport lighting system, not just as an isolated diagram.