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Calculating a light's visible range

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Postby Forchu » Thu Mar 31, 2005 3:30 pm


On Sankaty,Gay Head,Chatham,Nauset,Cape Cod,Boston,Graves,Thacher I.,White I.,Monhegan,Mt. Desert Rock,Petit Manan, and C. Forchu.


thanks I would love this info, please reply soon.
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Postby Terry_Pepper » Thu Mar 31, 2005 6:59 pm


Forchu,

What specific information are you seeking - maximum visible range, or something else?
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Postby Hersh » Thu Mar 31, 2005 10:23 pm


I don't understand what you're looking for either...
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Postby Forchu » Fri Apr 01, 2005 2:18 pm


M.V.R Maximum visible Range
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Postby island » Fri Apr 01, 2005 2:32 pm


If you want to determine visible range in nm of a lighthouse it can be calculated from the focal plane elevation. Multiply the square root of the focal plane height in feet by 8/7 (or by 1.14). The visible range listed in Light Lists assumes the viewers eye level to be at 15 feet above sea level so add 4.4 nm to the calculated nm.

For Cape F.

Square root of 123 ft focal plane = 11.1
11.1 x 8/7 = 12.7 nm
12.7 + 4.4 = 17.1 nm visible range.
Last edited by island on Fri Apr 01, 2005 2:44 pm, edited 1 time in total.
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Postby Maria » Fri Apr 01, 2005 2:44 pm


I knew I should have paid attention in Algebra class :?
No one ever told me it would come in handy for lighthousing.

8)

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Postby plebetkin » Fri Apr 01, 2005 2:47 pm


wait until you see the trig and calculus that Fresnel used for his light formulae
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Postby island » Fri Apr 01, 2005 3:38 pm


We are waiting. Where is it?
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Postby ron » Fri Apr 01, 2005 4:33 pm


doesn't bulb size, colour of lens (except LED), type of lantern and weather have more to do with this?
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Postby beachbum1616 » Fri Apr 01, 2005 4:53 pm


Please pardon my ignorance, but how does that equate into miles?
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Postby island » Fri Apr 01, 2005 4:55 pm


Ron.

The formula I posted was for visible range based on line of sight. The luminous range would be impacted by the factors you mentioned. Some lights may be seen beyond the visible range while others not seen that far depending on the light output.

A light with a red sector may have 14 miles visibility in the white and only 11 miles in the red. Green also would have a reduced visibility compared to white.

Weather conditions obviously impact visibility. Thick Maine Coast fog for example. Dust and or smoke particles will reduce the range.

Moisture, salt and dirt on the lens or on the storm panes reduces the output of the light, a common problem now with no keepers to attend to the daily cleaning.

A light with a red sector may have 14 miles visibility in the white and only 11 miles in the red.
Last edited by island on Fri Apr 01, 2005 5:29 pm, edited 1 time in total.
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Postby Terry_Pepper » Fri Apr 01, 2005 5:02 pm


Stephen,

One nautical mile equals 1.15077945 statute miles.
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Postby beachbum1616 » Fri Apr 01, 2005 5:22 pm


](*,)

Man, I have had a rough day. For some unknown reason, I had it in my head that nm meant nanometers. It never occured to me it meant nauticle miles.

#-o
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Postby island » Fri Apr 01, 2005 5:38 pm


Sorry Stephen, I should have described it better and not assume everyone would know what nm means. I should also have used NM not nm.

from http://www.unc.edu/~rowlett/units/dictN.html
nautical mile (nmi, naut mi, n mile, or NM)
a unit of distance used primarily at sea and in aviation. The nautical mile is defined to be the average distance on the Earth's surface represented by one minute of latitude. This may seem odd to landlubbers, but it makes good sense at sea, where there are no mile markers but latitude can be measured. Because the Earth is not a perfect sphere, it is not easy to measure the length of the nautical mile in terms of the statute mile used on land. For many years the British set the nautical mile at 6080 feet (1853.18 meters), exactly 800 feet longer than a statute mile; this unit was called the Admiralty mile. Until 1954 the U.S. nautical mile was equal to 6080.20 feet (1853.24 meters). In 1929 an international conference in Monaco redefined the nautical mile to be exactly 1852 meters or 6076.115 49 feet, a distance known as the international nautical mile. The international nautical mile equals about 1.1508 statute miles. There are usually 3 nautical miles in a league. The unit is designed to equal 1/60 degree [2], although actual degrees of latitude vary from about 59.7 to 60.3 nautical miles.[/url]
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Postby island » Fri Apr 01, 2005 6:00 pm


To knot or "naut" this up further:

knot (kn or kt) [1]
a unit of velocity equal to one nautical mile per hour. Knots are customarily used to express speeds at sea, including the speed of the ship as well as the speeds of the wind and of the current. The word comes from the former method of measuring a ship's speed, which involved use of a knotted cord called the log line. One knot equals about 1.1508 miles per hour, exactly 1.852 kilometers per hour, or 0.5143 meters per second. Since kt is the established symbol for the kilotonne, kn is the best choice as a symbol for the knot.

Some folks often refer to speed as knots per hour. This is not correct terminology.
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