LIGHTHOUSE - DEFINITION OF TERMS

	If you don't happen to be an experienced marriner, some of the terms John has used on this web site read like ancient Greek or Latin. To help make things a little clearer, I've done some research and put together a Table of Definitions. I'll be adding to this table occasionally, as I become aware of new terms that need defining.
www.lighthouse-photo.com
	Definition of Terms
Danielle Executive Assistant to the Webmaster

Light Characteristics			Example
Fixed	F	Fixed (always on) light	F R
Flashing	Fl	Period of light is shorter than the period of darkness. Flash rate less than 30 flashes/minute.	Fl W 6 sec
	LFl	Long Flashing. Period of light exceeds 2 seconds but is shorter than the period of darkness	LFl W 6 sec
	QFl	Quick Flashing. Period of light is shorter than the period of darkness. Flash rate exceeds 60 flashes/minute.	QFl R
Occulting	Occ	Period of light is longer than the period of darkness	Occ W
Isophase	Iso	Period of light is equal to the period of darkness	Iso W
Equal Interval	E Int	Period of light is equal to the period of darkness	E Int R
Alternating	Alt	A light that flashes 2 different colors in sequence	Alt WG 10 sec
Group Flashing	(2)	2 flashes followed by a period of darkness
	(X)	X flashes followed by a period of darkness	Fl W (3) 20 sec
	(X+Y)	X flashes followed by a period of darkness then Y flashes followed by a longer period of darkness	FL W (3+1) 20 sec
	(X+Y+Z)	X flashes followed by a period of darkness then Y flashes followed by a period of darknessy then Z flashes followed by a longer period of darkness	FL W (3+1+1) 20 sec
Morse Code	Mo	Light flashes a series of long and short flashes equal to a letter of the alphabet in Morse Code. Typically a white light used to mark an inlet, harbor entrance, channel entrance, or an isolated structure such as an oil platform. Also used occasionally in lighthouses in some countries.	Mo "R" W 15 sec
Flash Cycle Time	nn sec	the number of seconds it takes for the flash cycle to begin repeating itself. 6 seconds is the most common cycle time in the USA. 15, 20, and 30 seconds are commonly seen in lighthouses.

Light Colors
White	W	All navigation lights are white unless otherwise specified.
Red	R	Generally used to mark one side of the channel. {North America = Right -- International = Left}
Green	G	Generally used to mark the opposite side of the channel from a red light.
Orange	O	Used infrequently where the color is needed to distinguish the navigation light from other surrounding lights
Yellow	Y	Used on special purpose or informational bouys. May have any characteristic appropriate to its use. Not used in lighthouses.
Sectors		Sectored lights are generally used in lighthouses used where approaching the light from certain directions may be dangerous. WR = White w/ Red sector(s) WRG = White w/ Red and Green sector(s)
Red	R	A red sector is used to indicate a hazard to navigation (Shalow water, reef, rocks, wreck, small island, etc.)
Green	G	A green sector (not used in the USA) is used to indicate a preferred channel.

Lighthouse Range		Example
Nominal Range	The distance the light can be seen on a reasonably clear night. Range is determined by the brilliance of the light and/or the height of the light above the water.
Unit of Measure	The international measure for the range of a light is nautical miles. Statute miles are used in inland lakes in the USA.
Metoralogical Visability	The range of a light is calculated based on a metoralogical visibility of 10 miles.
Focal plane	The verticle distance from the center of the lens to the water (average level of high tide). The international unit of measure is meters. (feet in the USA)
Candlepower	Measure of the briliance of the light after it passes through the lens.	T
On a very clear night, most lighthouses can be seen well beyond their nominal range.

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