Obstruction lighting

Aircraft and tall buildings are a dangerous combination. Aircraft need a clear path to a certain height for take off and landing on the airfield. Any obstruction to the takeoff and landing can be disastrous for both the people in the air and on the ground. Thus, International Civil Aviation Organization (ICAO) set requirements for Obstruction Lighting

To prevent disasters, obstruction lighting is installed on tall structures to warn pilots to avoid the said structures. The Federal Aviation Administration (FAA) and the International Civil Aviation Organization (ICAO) set out regulations & gave recommendations for installing aviation warning light systems on tall structures both domestically and internationally.

Any structure that exceeds 200 feet above the ground level needs to be marked prominently with aircraft warning lights. Industrial chimneys, windmills & turbines, smokestacks, water tanks, pylons, cranes, and broadcast masts & towers that meet or exceed this height must be visible to aircraft at any time during the day or night.

Navigation light

navigation lights
photo credit: www.plastimo.com

Aircraft use collision avoidance lighting systems to warn other aircraft of their presence. These lights include landing lights, red or white flashing beacons, wingtip strobes, and wingtip navigation lights. The wingtip navigation lights are required to consist of red light on the left wingtip and a green light on the right wingtip. Landing lights are used during the descent and approach to landing and at other times if deemed necessary by the flight crew or operator.

Use of obstruction lighting and positioning

obstruction lighting and positioning
photo credit: clampco.it

These lights are attached to any tall structure such as broadcast masts and towers, water tanks located on a high elevation, electricity pylons, chimneys, tall buildings, cranes, and wind turbines. Shorter structures located close to airports may also require lighting; an example of which is the south scoreboard at Lambeau Field in Green Bay, Wisconsin built-in 2013, the tallest structure in the general area of nearby Austin Straubel International Airport.

The ICAO requirements for Obstruction Lighting are adopted worldwide, for aviation warning lamps’ performance and characteristics.

Obstruction lights arrangements are in clusters of two or more around the structure at specific heights on the tower. Frequently there will be a set of lights at the top, and then one or more sets equally spaced down the structure. The United Kingdom’s Belmont mast has nine red lamp clusters spaced equally along with the mast’s full height.

Non-standard aircraft warning lights

Aircraft warning lights (AWL) are also required to have a specific beam pattern, light intensity, light color, and a number of lights based on international regulations and national standards. The structure’s AWL systems setup will depend on local terrain features, weather patterns, geographical locations, and the shape & layout of the structure or surrounding structures that need to be illuminated.

In technical terms, aircraft warning lights are high-intensity lighting devices attached to tall structures to avoid aircraft collisions. These devices make structures highly visible to aircraft and are useful at night and day in all weather conditions. These lights need to be bright enough to be visible for miles around the structure

Types of Obstruction Lights

According to the ICAO Requirements for Obstruction Lighting, the lights used in an AWL system must be distinguishable by a set of parameters: beam patter, color, intensity, and flash rate. There are three main groups to consider as stated by the ICAO:

⦁ Low-intensity obstruction lights: these lights should be useful where the object height above the surrounding ground is lower than 45 m.
⦁ Medium intensity obstruction lights: should be used where the object height above the surrounding ground level is higher than 45m.
⦁ High-intensity obstruction lights: these lights are useful to indicate an object’s presence if its height above the level of the surrounding ground exceeds 150m.

In countries like the United States and Canada, there are different types of lights:

⦁ Obstruction lights (that permanently illuminated)
⦁ Red beacons/red strobes
⦁ High-intensity white (strobe) lights
⦁ Medium-intensity white (strobe) lights

Red lamps (or beacons) usually use incandescent filament bulbs. To optimize their short lifespan, they come with a rugged design and are run on less average operating power. It was then replaced by an array of high-power red LEDs instead of incandescent bulbs. LED lamps have a longer lifespan than traditional bulbs, reducing maintenance costs and more reliability. Manufacturers have also developed medium-intensity white strobes LED light to replace xenon. Xenon flashers, while more visually brighter, need to be replaced frequently and have become obsolete.

Distinctive lighting provides a universal recognition for showing the presence of obstructions, especially at night or in low visibility conditions. An obstruction light, or a group of lights, is usually red or white, visible 360°, and frequently installed on top of structures or mountain tops to warn pilots of a possible collision.

Obstruction is identifiable by flashing aviation red beacons (20 to 40 flashes per minute) and steady burning aviation lights during nighttime operations and with aviation orange and white paint as daytime markings. Obstructions are equipped with high-intensity white obstruction lights during the daytime, with reduced intensity at twilight and nighttime operations.

Medium-intensity white obstruction lights operate during the daytime and twilight, automatically reducing light intensity for nighttime operation. Once this system is used on structures 500 ft (150 m) AGL (above ground level) or less in height, other methods of identifying the obstruction are removed. But other regulations require aviation orange and white paint is always required for daytime marking on structures exceeding 500 ft (150 m) AGL. Dual lighting and flashing high-intensity lights can also be used during the daytime. And at night, flashing aviation red beacons and steady burning aviation red lights are utilized. Lighted markers are available for increased night visibility of high-voltage (69 kV or higher) transmission high tension wires. Lighted markers provide visibility both day and night.
Red lights are easily found in urban areas since it is easier for pilots to spot them from above. White strobes that flash nonstop may also be used in urban areas. It recommended that flashing white strobe lights should not be used in densely populated areas, as the lights can merge with background lighting during nighttime, making it difficult for pilots to spot them, expanding the hazard.

aerial marker
photo credit: tc.canada.ca

There are a medium-intensity white strobe and a high-intensity white strobe. Medium-intensity white strobes are used on structures between 200 and 500 feet (61-152.4 meters). A medium white strobe is used on a structure greater than 500 feet (152.4 meters). It must be painted. The common medium white strobe flashes 40 times per minute with an intensity of 20,000 candelas for daytime/twilight and 2,000 candelas at nighttime.

Rules on structure obstruction paint

ICAO Requirements for Obstruction Lighting standards require towers and masts painted with equal length stripes of international orange and white paint through their entire length to make it more visible during daytime. The paint requirement is put on towers over 200 feet tall but may vary from state to state and near airports internationally.

Because such the paint regulation is costly to apply, antenna towers and masts are built at heights just below the regulated level. Additionally, antenna towers and masts often have other aircraft warning systems located at equal distances, elevations, and tops. These may include high powered strobe lights or LED lights in either red, white, or both colors in an alternating pattern. Red light is utilized at night, while a white strobe is used during daylight hours.

Use of high-intensity white strobe lights

A high-intensity white strobe is used on structures taller than 700 feet (213.4 meters). These lights have the highest visibility for both day and night. Unlike a medium strobe, a high-intensity strobe does not have 360° coverage; 3 high strobes are installed at each level.

The advantage of the high-intensity white strobe that it reduces maintenance costs hence no painting. If the structure has an antenna at the top greater than 40 feet, a medium-intensity white strobe light is placed above it. The high white strobe flashes 40 times per minute, at an intensity of 270,000 candelas for daytime, 20,000 candelas at sunset, and 2,000 candelas at nighttime.

Dual lighting system

Dual lighting system
photo credit: cdn.flightlight.com

A dual lighting system is a structure equipped with white strobes for daytime use, and red lights for nighttime use. In urban areas, these are preferred since painting the structure is not needed. Another advantage is that when the uppermost red lights malfunction, the lighting switches onto its backup lighting system, using the white strobes. In the US and Canada, red incandescent beacons are being phased out from service and replaced with red strobes or red LEDs.

For high-tension power lines, white strobes flash 60 times per minute with the same intensity. Unlike ordinary white strobes, these strobes are designed not to flash simultaneously. The FAA-mandated pattern is middle, top, and bottom to provide “a unique signal that pilots should interpret as a warning that high tension wires are in the vicinity of the lights.”

Transmission towers

The lights can be powered from the electric field surrounding the energized conductor on electric transmission towers or the magnetic field produced by current through the conductor. The first method takes advantage of the high electric potential gradient around conductors. The second method uses Faraday’s law of induction involving magnetic flux flowing through a circuit that powers up the warning light.

Anything that hinders or prevents movement, particularly anything that endangers or prevents the passage of a vessel or aircraft. Usually refers to an isolated danger to navigation, such as a submerged rock or pinnacle in the case of marine navigation, a tower, tall building, mountain peak, and so forth, in air navigation.

Location of Lights

The number of light units will depend on the diameter & shape of the structure. The light arrangement allows the object to be seen from every angle in azimuth, giving a clear indication of the structure’s size, shape, and diameter. The FAA has set up structure guidelines that state that any object with a diameter of up to 6m will require three lights, and any object with a diameter of greater than 6m will need four lights.

Reliable obstruction lights are vital in making high-rise buildings, towers, and wind turbines visible to passing aircraft. At night, twilight, and stormy weather and poor visibility, obstruction lighting ensure that tall assets are always safely visible to aviation.


Tall buildings and structures have always been a danger to airline traffic. Government safety agencies responsible for the welfare of the people in and under the skies must regulate how to put warning systems. Following ICAO Requirements for Obstruction Lighting warning beacons for the airline pilots can know what to avoid and safely land their aircraft.

As lighting obstruction technology has produced better and longer-lasting strobe lights, there should also be a better means to track other obstructions that could endanger airline traffic, be it natural or human-made.

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