Structure using a white strobe
Structure using a Red/White Strobe
Closeup of an aircraft warning light on top of a highrise in Changzhou, China
Structure using high intensity white lights and a medium intensity white strobe
The lights generally come in two forms:
Red lamps that are either constantly illuminated or turn on and off slowly in a cycle of a few seconds.
White xenon discharge flashers.
Both types were in use in the United Kingdom until recently, however new regulations stipulate the use of red lamps at nighttime only. Xenon flashers are therefore gradually being phased out.
In the United States and Canada, there are several types of lights:
Obstruction lights (that are constantly illuminated)
High Intensity White (Strobe) Lights
Medium Intensity White (Strobe) Lights
Traditionally, red lamps (or beacons) use incandescent filament bulbs. In order to improve the otherwise quite short lifespan, they are made with a ruggedised design and are run below normal operating power (under-running). A recent development has been the use of arrays of high power red LEDs in place of incandescent bulbs, which has only been possible since the development of LEDs of sufficient brightness. LED based lamps have a significantly longer lifespan than incandescent bulbs, thus reducing maintenance costs and increasing reliability. Several manufacturers have also developed medium intensity white strobes based on LED technology to replace Xenon.
Xenon flashers, whilst more visually impressive, tend to require frequent replacement and so have become a less favoured option. However, with the advent of LEDs, white strobes are still somewhat desired.
It is common to find structures with white xenon flashers/white strobes during the daytime, and red lights at night. Red lights are commonly found to be used in urban areas, since it is easier for pilots to spot them from above. White strobes (that flash 24/7) may also be used in urban areas. However, it has been recommended that flashing white strobes should not be used in densely populated areas; the lights usually merge with background lighting at nighttime, making it difficult for pilots to spot them and thereby aggravating the hazard. In addition, residents near the lit structure will complain of light trespass.
In rural areas, red beacons/strobes may also be used during nighttime. However, white strobes are (sometimes) preferred since it reduces maintenance cost (i.e. no maintenance of painting, no red side lights) and there are no background lights that would blend with the strobes.
For white strobes, there is a medium intensity white strobe and a high intensity white strobe. Medium Intensity White Strobes are usually used on structures that are between 200500 feet (61-152.4 meters). If a medium white strobe is used on a structure greater than 500 feet (152.4 meters), the structure must be painted.
The common medium white strobe flashes 40 times in a minute, at an intensity of 20,000 candelas for daytime/twilight, and 2,000 candelas at nighttime.
A high intensity white strobe light is used on structures that are greater than 500 feet (152.4 meters). These lights provide the highest visibility both day and night. Unlike a medium strobe, a high intensity strobe doesn't provide 360 coverage; this requires the use of at least 3 high strobes at each level. On the other hand, it reduces maintenance costs (i.e. no painting). If the structure has an antenna at the top that is greater than 40 feet, a medium intensity white strobe light must be placed above it rather than below.
The common high white strobe flashes 40 times in a minute, at an intensity of 270,000 candelas for daytime, 20,000 candelas at twilight, and 2,000 candelas at night-time.
Dual lighting is where a structure is equipped with white strobes for daytime use, and red beacons/strobes for nighttime use. In urban areas, these are commonly preferred since it usually exempts a structure from the requirement of having to be painted. One advantage to the dual system is that when the uppermost red lights fail, the lighting switches onto its Backup lighting system, which uses the white strobes (at its night intensity) for nighttime. In the United States and Canada, red beacons are slowly going out of commission and being replaced with red strobes. In addition, some medium strobes are equipped to flash the white light for daytime and red light for night in a single strobe (unlike the old type which had two different lights).
For high tension power lines, the white strobes are equipped to flash 60 times per minute, using the same intensities as stated above. Unlike the common white strobes, these strobes are specified not to flash simultaneously. The flash pattern should be middle, top, and bottom to provide "a unique system display".
An antenna tower stands 446 feet tall in Springfield, MO with its red and white aircraft warning paint clearly visible in the setting sun.
Aircraft use collision avoidance lighting systems to warn other aircraft of their presence. These lights include landing lights, white beacons, wingtip strobes, and wingtip navigation lights. The wingtip navigation lights are required to consist of a 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.
These lights can generally be found attached to any tall structure such as broadcast masts and towers, water tanks located on high elevation, electricity pylons, chimneys, tall buildings, cranes and wind turbines. Shorter structures that are located close to airports may also require lighting. The International Civil Aviation Organization (ICAO) sets standards, usually adopted worldwide, for the performance and characteristics of aviation warning lamps.
Lights are usually arranged in clusters of two or more around the structure at specific heights on the tower. Frequently there will be a set at the top, and then one or more sets equally spaced down the structure. England's Belmont mast (the tallest construction in the European Union) has nine clusters of red lamps spaced equally along the full height of the mast.
Non-standard aircraft warning lights
On some tall structures there are or were non-standard aircraft warning lights installed
The mast of Deutschlandsender Herzberg/Elster had no aircraft warning lamps installed. It was instead lit by skybeamers mounted on small masts near the tower. This method was chosen as the mast was a mast radiator insulated against ground and for feeding the lamps on the mast otherwise special devices like Austin transformers would be required.
Stuttgart TV Tower carries rotating lamps like used on lighthouses. Such lamps were also used on other towers in earlier days.
Blosenbergturm in Beromnster has a rotating lamp above the cabin. In opposite to Stuttgart TV Tower it is less bright and only operated in the dawn.
The main mast of Mhlacker radio transmitter and the former Konstantynow Radio Mast has or have also aircraft warning lights at the outmost bases of their anchor guys.
Conductor marking lights and Balisors are sometimes used for marking power lines.
The Obstacle Collision Avoidance System allows the standard lights to remain off until an aircraft is in within a given radius, allowing for a significant decrease in light pollution. The OCAS system also provides audio warnings.
Aircraft warning paint usually consist of red and white paint at equal lengths on the antenna tower or mast. These sections of paint are usually only required on towers over 300 feet tall, but may vary from state to state and near airports internationally. These paints are usually expensive to apply and that's why the perferred height of an antenna tower or mast is usually right under that certain height requirement. These antenna towers or masts that have these paintjobs usually almost always have some sort of aircraft warning feature located at equal sections and at the top of the antenna tower or mast. These are usually high powered strobe lights or LED lights that are either red, white, or both colors (differing in color at different parts of the day, red most likely being at night and a white strobe in the day.
Advisory Circular 70/7460-1K from the United States Federal Aviation Administration
The Transmission Gallery: Close up of LED warning lamp array on the Membury mast
The Transmission Gallery: Belmont mast - includes night shot showing the nine sets of warning lamps
Obstacle Collision Avoidance System (OCAS) - Enhanced Standard Lighting by eliminating unnecessary light pollution
Aircraft warning lights gallery
Aircraft warning lights video and models: LIOL-B (L810), MIOL-B (L864), MIOL-A (L865)
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