What are Low-intensity Obstruction Lights?
Steady red lights that mark buildings, low masts, cranes and other fixed objects under about 45 m, so pilots can see them at night.
Low-intensity obstruction lights are the lowest of the three obstacle-light classes. They are fixed (steady) red lights, used on lower fixed objects where a modest light is enough to make the object visible at night.
Two types cover fixed objects. Type A has a minimum peak intensity of about 10 cd. Type B is brighter, at about 32 cd, and is used where Type A would not be conspicuous enough.
Lights are placed at the highest points and edges of the object, in numbers that let a pilot see the object from every direction. On taller structures, additional lights are added at intermediate levels. Above about 45 m, medium- or high-intensity lights are normally needed instead, and so can an extensive object under 45 m, where a brighter light is needed to show its extent.
| Light | Mode | Peak intensity (typical) | Where it is used |
|---|---|---|---|
| Type A | Fixed red | About 10 cd minimum | Lower, smaller objects under about 45 m |
| Type B | Fixed red | About 32 cd minimum | Where Type A is not conspicuous enough; also paired with medium-intensity Type B on taller objects |
| FAA L-810 | Steady red | About 32 cd | FAA low-intensity red light, structures up to about 150 ft (45 m); also on lower tiers of some taller structures |
Find the high points
Identify the highest points and edges of the object, as seen from where aircraft approach.
Fit top lights
Place lights at the top, with enough of them that at least one can be seen from any direction.
Add tiers if needed
On taller structures, add intermediate levels so the object is shown from top to base.
Control and check
Switch the lights on at dusk, usually by photocell, and monitor them so a failed lamp is found and fixed.
A red obstacle light is not the same as the other red lights on an airfield, and low-intensity red is not the same as flashing red. Tell them apart by mode and purpose:
- Fixed Red (Low A / B)→ steady light on a lower fixed object, under about 45 m
- Flashing Red (Medium B)→ brighter, flashing light for taller objects
- Runway End / Stop Bar Red→ airfield lights that tell an aircraft where to stop
Also remember that a low-intensity light works at night only. By day, the object relies on its marking where marking is required.
ICAO Low-intensity Obstacle Lights
ICAO Annex 14 Volume I, Chapter 6, provides low-intensity obstacle lights Type A and Type B for fixed objects. Both are fixed red. Type A has a lower minimum peak intensity than Type B. They are used on lower objects, typically under about 45 m above ground level, and are placed to show the highest points and edges of the object so that it is visible from every direction. Where low-intensity lights would not be adequate, or an earlier warning is needed, medium- or high-intensity lights are used instead. Types C and D in the same chapter are for vehicles and other mobile objects and are outside this entry. Type E, a flashing red 32 cd light, is used as the tower tier on large wind turbines and is covered in the wind-turbine entry. Take the type, number and layout from the regulator's determination and the current edition of the standard.
FAA Low-intensity Obstruction Lights
The FAA covers this in AC 70/7460-1, Obstruction Marking and Lighting. Its low-intensity light is the L-810, a steady-burning red light used on lower structures and, in some lighting styles, at the lower levels of taller ones. Confirm the current edition of the advisory circular, and the lighting style and fixture the FAA determination requires for your structure.
Frequently Asked Questions
Q1What are low-intensity obstruction lights?
Low-intensity obstruction lights are steady red lights fitted to lower fixed objects, such as buildings, low masts and cranes, so that a pilot can see them at night. They are the lowest of the three obstacle-light classes.
Q2What is the difference between Type A and Type B?
Both are fixed red. Type A has a lower minimum peak intensity, about 10 cd. Type B is brighter, about 32 cd. Type B is used where a Type A light would not be conspicuous enough, and it can also be paired with medium-intensity Type B lights on taller objects.
Q3How tall an object do low-intensity lights normally cover?
Typically objects under about 45 m above ground level. Above that, medium- or high-intensity lights are normally needed. The height band is a guide, and the regulator's determination for the object governs.
Q4Do low-intensity obstruction lights work by day?
No. A steady red light of this intensity is a night light, usually switched on at dusk by a photocell. By day the object depends on its marking, such as paint, flags or markers, where marking is required.
Q5Why are they steady rather than flashing?
A steady red light is the standard signal for a lower fixed hazard. Flashing red is normally the medium-intensity (Type B) signal, where the light needs more conspicuity at greater height and distance. The one low-intensity flashing red, Type E, is reserved for wind-turbine towers.
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