International Civil Aviation Safety Specifications for Low Intensity Beacons
According to ICAO International Civil Aviation Organization, a body overseeing International Civil Aviation Safety, tall aviation obstacles as Antennas, Telecom towers, Met Towers, Buildings, etc… must be signaled among other means, by installing Lights in those structures, following very specific recommendations.
Low Intensity Lights Type A or B are used if the object is “less extensive” and its height above the surrounding terrain is less than or equal to 45m. The most common Low Intensity beacons are Type A and Type B (according to ICAO terminology).
Luminous intensity of the beacons
Type A nomenclature refers to the intensity of light, which for beacons in this mode will be equal to or greater than 10 Candelas.
Low Intensity Type B beacons are those of intensity equal to or greater than 32 candelas.
Modality of operation
Both types must be red color, in fixed mode and must be shining during the night, in the 360º of Azimuth evenly around the point of light.
In addition, a specific characteristic is needed in order to minimize the light pollution produced by the beacon: The light must be concentrated, mostly, from its horizontal (0º) to an opening of 10 degrees. The light forms an opening angle of only 10º of amplitude around it, being visible from a long distance by aircraft that could fly on a collision course with the object.
At aerodromes, Type C low-intensity lights with blue or yellow flashing lights will be used to signal vehicles and mobile objects, except for aircraft, and Type D lights will use yellow flashes to signal the guide vehicles.
Scope of the light in Low Intensity beacons:
How far the luminous beacons light should be seen? The answer is not simple, since this vision depends on the Atmospheric Transmissivity. This is the proportion of light that remains after traveling a nautical mile. For example, an Atmospheric Transmissivity of 0.74 corresponds to the retention of 74% of the intensity of light at a nautical mile distance. Since said transmissivity depends on the meteorological conditions and these are changing, the light of a beacon will not always be visible at the same distance. For this reason, “type” scopes are established for different situations of transmissivity.
If the weather conditions are very clear (0.85T) the range will be higher than 8.5Km.
In contrast, in situations of fog or fog, the scope will be lower.
For obstacles over 45m height, up to 150, Medium Intensity, 2,000 candelas, light signaling beacons will be used. When the height is greater, High Intensity beacons will be used.