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An example of a complete light characteristic is "Gp Oc(3) W 10s 15m 10M". This indicates that the light is a group occulting light in which a group of three eclipses repeat every 10 seconds; the light is white; the light is 15 metres above the chart datum and the nominal range is 10 nautical miles.
The Hoy High Light, known as Graemsay Island Range Rear, is 33 metres (108 ft) high and has a white and red occulting light every 8 seconds depending on the directions. [9] [10] The Hoy Low Light (Graemsay Island Range Front) is 12 metres (39 ft) high and is distinguished by a white isophase light every 3 seconds.
The light was automated in 1979. [2] [11] Today, the lighthouse displays an occulting red light with a four-second period, having a nominal range of 12 nautical miles. [4] During the navigation season that runs from April 1 to November 1, the fog signal sounds a two-second blast every fifteen seconds. [4] [12]
The lighthouse design is similar to the 1934 design at Robertson's Point. Its light characteristic is occulting green light with a cycle of three seconds (Oc.G. 3s), the same as Robertson Point Light. [1] [2] [4] [5] It is mounted on a rock and connected to the shore by a footbridge.
The lighthouse at Fourteen Foot Shoal was named to note that the lake is only 14 feet (4.3 m) deep at this point, which is a hazard to navigation, ships and mariners.. This light is located at the northern end of Lake Huron, Michigan, US, where it is necessary for boats heading to Chicago to pass through a narrow strait and still avoid shallow water.
They either flash Morse code "A" (di-dah), or one long flash, occulting (more light than dark) or isophase (equal light and dark) every 10 seconds (L Fl 10s). [ 2 ] In the United States, safe water marks are printed with the initials of their associated waterways or localities.
The lighthouse was converted to electric in 1970. The character of the light was occulting 20s (on for 15 seconds and off for 5 seconds). This was altered on 15 August 1993 to Fl WR 3s (one white and red flash every three seconds). From April 1978 the light has also been exhibited in conditions of poor visibility while the fog signal was sounding.
The first revolving light was fitted to the Swin Middle lightvessel in 1837: others used occulting or flashing lights. White lights were preferred for visibility though red and very occasionally green (as with the Mouse lightvessel) were also used. [12]