Editing Leading lights

{{short description|Navigational tool}}
{{for|the racehorse|Leading Light}}
{{more citations needed|date=May 2012}}
[[Image:NantucketRangeLites.jpg|thumb|right|[[Nantucket Harbor Range Lights]]<ref name=cgll>{{cite uscgll|1|2009|135}}</ref> The [[dayboard]]s are type KRW, see below.]]
[[Image:Bremerhaven Unterfeuer 1.jpg|thumb|[[Bremerhaven Lighthouse|A pair of leading lights in Bremerhaven]], Germany, with the rear light in a proper lighthouse and the front light on a smaller tower. No standardised markings are used here.]]

'''Leading lights''', also known as '''range lights''' in the [[United States]], are a pair of light beacons used in [[navigation]]<ref>{{cite web|url=http://www.ialathree.org/dictionary/index.php?title=Leading_Lights_%28G.B.%29 |title=Dictionary of the International Association of Lighthouse Authorities |publisher=[[International Association of Lighthouse Authorities]]}}</ref> to indicate a safe passage for vessels entering a shallow or dangerous channel; they may also be used for [[position fixing]]. At night, the lights are a form of [[Piloting#Piloting in channels and rivers|leading line]] that can be used for safe navigation. The beacons consist of two lights that are separated in distance and elevation, so that when they are aligned, with one above the other, they provide a bearing. Range lights are often illuminated day and night.

In some cases the two [[beacons]] are unlighted, in which case they are known as a ''range'' in the United States or a ''[[Navigational transit|transit]]'' in the UK. The beacons may be artificial or natural.

==Operation==
Two lights are positioned near one another. One, called the front light, is lower than the one behind, which is called the rear light. At night when viewed from a ship, the two lights only become aligned vertically when a vessel is positioned on the correct bearing.<ref>{{cite book |last1=Bowditch |first1=Nathaniel |title=The American practical navigator : an epitome of navigation |date=2002 |publisher=Paradise Cay Publications |location=Bethesda, Md. |isbn=9780939837540 |page=64 |edition=2004}}</ref>

During the day, the lights may not easily be seen and therefore leading lights are often fitted with secondary visual aids, e.g. large red flags with wide black lines running down them. When both red flags and black lines line up, the navigator knows that the vessel is on the correct bearing. The structures are usually painted to make them more prominent.

Some major rivers, such as the [[Elbe|Elbe River]] in [[Germany]], have a series of leading lines. When it is necessary to make a turn, the navigator lines up the next pair of leading lights. This provides guidance from [[Hamburg]] to the sea, using successive pairs of leading lights.<ref>{{cite book |last1=Wendemuth |first1=Ludwig |title=The port of Hamburg, with plans, charts and numerous illustrations |date=1927 |publisher=Meissner & Christiansen |location=Hamburg |oclc=586327105 |page=204}}</ref>

Leading lights were used in Great Britain as early as 1763 to mark the [[Port of Liverpool]].<ref>{{cite book|title=Lighthouses of Liverpool Bay |first=John |last=Robinson |first2=Diane |last2=Robinson |publisher=[[The History Press]] |year=2007 |isbn=978-0752442099}}</ref> The first set of range lights in the [[United States]] were privately established by subscription at [[Newburyport, Massachusetts|Newburyport Harbor]] in [[Massachusetts]] in 1788.<ref>{{cite book |last1=Roberts |first1=Bruce |last2=Shelton-Roberts |first2=Cheryl |last3=Jones |first3=Ray |title=American lighthouses : a comprehensive guide to exploring our national coastal treasures |date=2012 |publisher=Globe Pequot Press |location=Guilford, Conn. |isbn=9780762779604 |edition=3rd}}</ref>

Leading lights are sometimes designed to be movable, allowing their position to be shifted in the event of a change in the safe channel; these include one at [[Hilton Head Range Rear Light|Hilton Head, South Carolina]], the original [[Chatham Light]], and the [[Nantucket Beacon]], predecessor to the Nantucket Harbor Range shown above.

==Gallery==
<gallery>
Image:NOAA Chart 13296 detail showing Range.png|[[Doubling Point Range Lights]] on NOAA chart 13296.
Image:USCG Daymarks.png|The twelve standard dayboards used on [[USCG]] ranges.
Image:Margaree Harbour Range Lights.jpg| Range lights at [[Margaree Harbour, Nova Scotia]].
File:Seili Leading Lights in Archipelago Sea in Finland.JPG|Marking the approach to the island of [[Själö|Seili]], Finland
</gallery>

==See also==
{{Portal|Engineering}}
*[[Daymark]]
*[[Sector light]]
*[[PEL sector light]]
*[[Visual approach slope indicator]], similar lights used in aviation to guide pilots to the right approach angle for landing
*[[Moiré pattern#Inogon light|Inogon light]]

==References==
{{Reflist}}

==External links==
{{commons category-inline|Leading lights}}

{{Lighthouses}}

{{DEFAULTSORT:Leading Lights}}
[[Category:Navigational aids]]
[[Category:Lighthouses]]
[[Category:Maritime signalling]]