What are HIRL, MIRL and LIRL?
The three intensity classes of runway lights. The class fixes how bright the lights can be and how many brightness steps they have, and it is chosen to match the runway and the weather it must work in.
A runway edge has to be seen in clear dusk and in thick fog, and one brightness cannot do both well. The intensity class is the design decision that says how bright the lights can be, so a precision runway and a small visual strip are each equipped to their job.
1HIRL: for precision and low-visibility runways
High intensity runway lights are the brightest class and normally have five brightness steps. They are used where the runway supports precision approaches and low-visibility operations, and where the pilot needs strong edge guidance at the end of the approach.
2MIRL: for non-precision and night runways
Medium intensity runway lights are fitted where the operations are lower demand, such as runways with non-precision approaches or regular night use in moderate conditions. They typically have three steps.
3LIRL: for basic visual runways
Low intensity runway lights are the simplest class, typically with a single step, used on small runways with visual operations. They show the edge without the cost and power of a high-intensity system.
4Class and step are different things
The class is chosen once, at design. The step is set by the constant current regulator, which raises or lowers the series circuit current as the weather and the tower's instructions change. A higher class gives more steps, so finer control, over a higher brightness range. On a 6.6 A series circuit a three-step regulator typically runs at 4.8, 5.5 and 6.6 A, and a five-step regulator at 2.8, 3.4, 4.1, 5.2 and 6.6 A (FAA AC 150/5345-10).
| Class | Intensity | Typical runway | Brightness steps (typical) |
|---|---|---|---|
| HIRL | High | Precision approach, low visibility | 5 |
| MIRL | Medium | Non-precision approach, night use | 3 |
| LIRL | Low | Basic runway, visual operations | 1 |
Frequently Asked Questions
Q1What do HIRL, MIRL and LIRL stand for?
High Intensity Runway Lights, Medium Intensity Runway Lights and Low Intensity Runway Lights. They are the three intensity classes used for runway edge lighting, and the class says how bright the lights are able to be.
Q2Which runways use HIRL?
HIRL is normally used on runways that support precision approaches and low-visibility operations, where pilots need bright, clear edge guidance. Which class a runway needs follows from the approach and the operations the aerodrome supports.
Q3Which runways use MIRL and LIRL?
MIRL is typically used on runways with non-precision or basic instrument approaches and on runways used at night in moderate conditions. LIRL is typically used on smaller, basic runways with visual operations. Check the applicable standard for the runway in question.
Q4How many brightness steps does each class have?
Typically five for HIRL, three for MIRL and one for LIRL, although the exact arrangement depends on the standard and the design. The steps are set by the constant current regulator, so more steps mean finer control of brightness.
Q5Is the intensity class the same as the brightness step?
No. The class is a design choice that fixes the brightness range of the fixtures. The step is the setting the CCR is running at right now, and it moves the brightness up and down within that range.
Q6Are HIRL, MIRL and LIRL ICAO or FAA terms?
They are FAA class names. ICAO Annex 14 does not use these class names: it requires variable-intensity runway edge lights and sets their photometric performance in Appendix 2, in isocandela diagrams that depend on runway width, so confirm which standard and which wording your project follows.
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