Alternating Light
A light showing different colours alternately.
Atmospheric Transmission Factor (Transmissivity)
A quantity characterising the transparency of the atmosphere to light emitted from a source. The atmosphere absorbs some of the emitted light. The amount of absorption depends upon prevailing atmospheric conditions. The atmospheric transmission factor (T) indicates the light transmission per nautical mile through the atmosphere.
Character
The properties of a light that distinguish its appearance.
Direction Light
A light showing over a very narrow sector, forming a single leading light. This sector may be flanked by sectors of greatly reduced intensity or by sectors of different colours or character. Direction lights are also used to mark the limits of areas.
Eclipse
An interval of darkness between appearances of a light.
Effective Intensity
The luminous intensity of a flashing light calculated (by the Schmidt-Clausen Method) as a function of time during the course of a flash.
Fixed Light
A light showing continuously and steadily.
Flash
A relatively brief appearance of a light, in comparison with the longest interval of darkness in the same character.
Flashing Light
A light in which the total duration of light in a period is shorter than the total duration of darkness and the appearances of light (flashes) are usually of equal duration.
Geographical Range
The maximum distance at which light from a source can theoretically reach an observer, as limited only by the curvature of the earth, the refraction of the atmosphere, the elevation of the light, and the observers height of eye.
Group Flashing Light
Flashing light in which the flashes are combined in groups, each including the same number of flashes, and in which the groups are repeated at regular intervals.
Group Occulting Light
Occulting light in which the occultations are combined in groups, each group including the same number of occultations, and in which the groups are repeated at regular intervals.
Intensity
The quantity (in candelas) of light reaching the eye of an observer after the light emitted by a source has propagated through a colour filter (if used) and a lens/lantern glazing.
Interrupted Quick-Flashing Light
Quick-flashing light in which the rapid alternations are interrupted at regular intervals by eclipses of long duration.
Isophase Light
A rhythmic light for which the alternations of light and darkness are of equal duration.
Leading Lights (Range Lights)
Two or more lights associated so as to form a leading line to be followed.
Luminous Range
The maximum distance at which a light can be seen at a given time, as determined by the effective intensity of the light and the meteorological visibility prevailing at that time. Luminous range takes no account of elevation, observers height of eye, or curvature of the earth.
Nominal Range
The luminous range of a light when the meteorological visibility is 10 sea miles (T=0.74).
Occulting Light
A light in which the total duration of light in a period is longer than the total duration of darkness and the intervals of darkness (eclipses) are usually of equal duration.
Period
The interval of time between the commencement of two identical successive cycles of the character of a rhythmic light.
Quick-Flashing Light
A light in which flashes are repeated at a rate of not less than 50 flashes per minute.
Rhythmic Light
A light that exhibits a sequence of intervals of light and darkness, repeated at regular intervals.
Sector Light
A light presenting different appearances, either of colour or character, over various parts of the horizon of interest to marine navigation.
Ultra Quick-Flashing Light
A light in which flashes are repeated at a rate of not less than 160 flashes per minute.
Very Quick-Flashing Light
A light in which flashes are repeated at a rate of not less than 80 flashes per minute. |
