Distance Titanic's lights could be seen


Mike Spooner

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Whist on the subject of lights. There seems some confusion how far one can see the Titanic lights in miles on a clear night.
Can some one tell me of the following in miles: Morse lamp, mask lights, side lights and passenger lights?
 
Nov 14, 2005
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According to this thread Dave Gittins states that Capt Lord said his Morse lamp could be seen at 10 miles. So I would think Titanics lamp could be seen that far if not a little more. As for the other lights I'm not sure. But if the whole ship was lit up, passenger lights and all I would think it would be that far also on a clear night. But thats just speculation on my part.
 

AlexP

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Whist on the subject of lights. There seems some confusion how far one can see the Titanic lights in miles on a clear night.
Can some one tell me of the following in miles: Morse lamp, mask lights, side lights and passenger lights?
I believe the Titanic's sidelights also had lenses, and yet Mr. Gibson testified he was able to see the sidelight only with the help of the glasses.
I believe it is reasonable to assume that the navigational lights of a much smaller and much older Californian were not nearly as bright as the lights of the Titanic.
 

Jay Roches

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I’ve seen that article before and wanted to find it again, so thanks for posting the link. Note just how dim the 32-candlepower, 402 lumen masthead light was: about as bright as a 40 W incandescent bulb. And yet, at sea in clear weather, it could be seen at considerable distance.

It may be safe to assume Californian’s lights were less bright, but they still needed to comply with Board of Trade standards. Is there any information about Californian’s lights? They could’ve been 1901-vintage oil lamps that just met the BoT requirements, or the masthead light could’ve been 32-candlepower, just like Titanic. It doesn’t necessarily follow that a bigger ship needs brighter lights. The line-of-sight data, given a lower bridge and mast, would of course differ.
 

AlexP

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It may be safe to assume Californian’s lights were less bright, but they still needed to comply with Board of Trade standards.
The standards were 5 miles for the masthead lights and 3 miles for the starboard lights I think.
Is there any information about Californian’s lights? They could’ve been 1901-vintage oil lamps that just met the BoT requirements, or the masthead light could’ve been 32-candlepower, just like Titanic. It doesn’t necessarily follow that a bigger ship needs brighter lights. The line-of-sight data, given a lower bridge and mast, would of course differ.
I believe they were electrical, but I do not think they had fancy lenses the Titanic's lights did. I assumed they were less bright because otherwise it is hard to explain why the Californian's lights were first seen from the Titanic some 50 minutes or more after the navigational lights of the Titanic were seen from the Californian.
 
Mar 22, 2003
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Can some one tell me of the following in miles: Morse lamp, mask lights, side lights and passenger lights?
It is not so simple Mike. I wish I had a chance to revise that article (GLTS | Masthead Light) I wrote sometime back on Titanic's masthead light and put it into a wider context. In short, the actual distance depends on essentially two things.
1. the nominal range of the light, which itself depends on the luminous intensity of the light source (after taking into account any magnification due to the dioptric lens that aim at concentrating the light in the vertical plane) for a given meteorological atmospheric condition such as 10 mile visibility for recognizable objects in daytime conditions, and
2. the luminous range, which is the expected range of the same light but under the current meteorological atmospheric condition.

For example, if the nominal range of a certain light is 10 miles under meteorological atmospheric conditions whereby in daytime recognizable objects could be seen as far as 10 miles away, then if that same light is seen at night under hazy meteorological conditions where recognizable objects could only be seen as far as 2 miles during daytime conditions, that light's luminous range would only be 3.5 miles on that night. On the other hand, if the same light is seen at night under very clear to extremely clear meteorological atmospheric conditions whereby recognizable objects could be seen as far as 27 miles away during daytime conditions, that light's nominal range works out to be 18 miles. Under infinite visibility conditions, that same light could be seen out to 45 miles.

Today's rules, masthead lights are designed for a luminous range of 6 miles or greater under a meteorological condition of 13 miles. Sidelights and stern lights are designed for a luminous range of 3 miles or greater under those same conditions.

So to really answer your question, you need to know what the meteorological atmospheric conditions were that night. I could not be too far off if it were varied between what is called very clear and exceptionally clear conditions.
 
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Mar 22, 2003
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Back in 1912 the minimum range for masthead lights was 5 miles, for sidelights 2 miles, and for a stern light 1 mile. These are all MINIMUM ranges. If I recall correctly, Morse signaling lights were not as bright as electric sidelights. Their lenses were a lot smaller too.
 

Mike Spooner

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Thanks for your reply Sam and it show its how not so straight forward as having to allow for atmospheric conditions! There was talk of a haze coming up to no doubt that too would of an impact on the matter as well.
It would appear the Morse code lamp has a greater range than the others at 10 miles. But again subject to atmospheric conditions!
Were the atmospheric conditions for the lighting range ever discussed at the inquires?
 
Mar 22, 2003
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Were the atmospheric conditions for the lighting range ever discussed at the inquires?
Only thing discussed were the rules then in effect, which of course were minimum requirements. It was understood however, that electric lights had greater ranges than the minimums. For the most part, the atmospheric conditions were extremely good that night since stars could be seen setting low down where the horizon would be. Usually, stars tend to extinguish before reaching the horizon because of the greater amount of air mass that their light has to pass through as they get lower and lower down.
 
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Is the distance you can see these lights also affected by the distance you can see to the horizon ?
Height of the observer, height of the light ?
 

Mike Spooner

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Hi Sam, not to put you on the spot, do you a have a feeling how far one could of seen any lights in miles, that if it was the Titanic?
I hate to say it the same question for Jim to, or any another seamen as well.
 

Doug Criner

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The question asked about for a clear night. The maximum visibility depends upon the range, the height of the light above sea level, and the height of the observer. The heights above sea level are important because of the earth's curvature. There are formulas published in nautical sites that cover this. Of course, it will also depend upon the brilliance of the light, the objective size of the binocular lens, and each human's own visual acuity.

What prompts the question?
 
Mar 22, 2003
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Is the distance you can see these lights also affected by the distance you can see to the horizon ?
Height of the observer, height of the light ?
Yes, of course, both. They determine the geographic range. The luminous range does not take that into account. The range that a given light could be seen will the the lesser of the two, the geographic or the luminous range.
Hi Sam, not to put you on the spot, do you a have a feeling how far one could of seen any lights in miles, that if it was the Titanic?
From the bridge of Titanic (height of eye 70 ft) the geographic range to a light at a height of 40 ft is 17 miles. That night, was very clear with stars seen setting right down to the horizon, so the real limitation appears to be geographic range for the most part.
As Doug asked, what prompts the question?
 

Jim Currie

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Hi Sam, not to put you on the spot, do you a have a feeling how far one could of seen any lights in miles, that if it was the Titanic?
I hate to say it the same question for Jim to, or any another seamen as well.
The only way anyone could be sure the vessel being seen was the Titanic at almost any range, would have been if her side was broad-on or nearly broad-on to the observer.

Observing a normal ship at a distance and approaching is difficult if you are depending only on the visibility of her navigation lights. However, you should all keep in mind that the Olympic class vessels were the biggest, most brightly lit vessel on the ocean at that time. Apprentice Gibson described what an ordinary passenger ship looked like at night: "I have seen nearly all the large passenger boats out at sea, and there was nothing at all about it to resemble a passenger boat. A passenger boat is generally lit up from the water's edge."

If any of you have ever seen a passenger ship at sea at night, you will immediately recognise what Gibson was describing. However, there was an extra bonus withe the Olympic boats...they had no less than five (5) rows of portholes on the side, which extended forward of and below, the masthead light, the red side light and the main deck to sea level.
Many of the forward cabins would have been in darkness before impact with the berg, but many... particularly in mess rooms and crew quarters... would be lit. The lit ones would be visible at about the same time the coloured sidelights were seen. After impact, the whole hull would be lit like a Xmas tree.
To answer your question: A passenger ship like Titanic approaching the stopped Californian on such a night, would have been very obvious at to those on Californian's upper bridge, 11 minutes before she stopped. That is when the lowest row of lit portholes on the starboard bow would have been visible.
Incidentally, Captain Lord said he saw the nearby vessel approaching from a lower deck and saw her green light after 11 pm. He guessed it was about 7 miles away. If that ship had been Titanic, he saw it at 11-22 pm, 8 minutes before she stopped. At that time there would be no possibility of mistaking a ship like Titanic and even a half- blind beggar would have seen her starkly at 4 miles away when she did stop. To suggest otherwise is ridiculously absurd to say the least.

Does the foregoing help to clear the air?
 

Mike Spooner

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What prompts the question? I would agree on modern cruise ships with many decks lights are a brighter rating than the Titanic was.
However didn't the Titanic start turn off lights by 11.00 for bed time? Therefore make it more difficult to recognise as a passage liner ship!
 

Georges Guay

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Titanic navigation lights range of visibility

Everyone knows by heart Article 2 issue forth the 1910 Regulations for preventing the collisions at sea. The masthead light had to be visible at a distance of at least 5 miles, the sidelights at a distance of at least 2 miles and the stern light from at least 1 mile. At least meaning not less than, at the minimum of, etc. If a candidate for the certificate of competency would present himself in front of a BOT nautical examiner and one of the questions to answer was; «According to the Rules, at what distance would you expect a masthead light to be seen in perfect visibility»; as of what I conclude from the evidences, the candidate would answer without hesitation 5 miles sir! Personally, I would not be entirely satisfied by that answer for the reason that a masthead light had to be visible at a distance of at least 5 miles onwards. There is quite a difference between could be seen and should or shall be seen. The range of visibility of a masthead light depends on the type of lantern (oil or electric), the type of lens (Plano convex or Fresnel), the intensity, the maintenance of the glass, the visibility, the height of eye of the observer, the observer visual acuity, the use of glasses, the abnormal atmospheric refraction, just to name a few.

Therefore, a masthead light had to be visible at a distance of at least, not less than or at the minimum distance of 5 miles in good visibility and virtually up to the geographical visible horizon in perfect visibility.

- Boxhall:
«I thought she was about 5 miles, and I arrived at it in this way. The masthead lights of a steamer are required by the board of trade regulations to show for 5 miles, and the signals (sidelights) are required to show for 2 miles. I saw the side lights. Whatever ship she was had beautiful lights. I think we could see her lights more than the regulation distance, but I do not think we could see them 14 miles.» Not to show for 5 miles but had to be visible at a distance of at least, not less than or at the minimum distance of 5 miles.

- Groves:
8419. What is the average range of an ordinary ship's sidelight? - Two miles.
8420. And the masthead light? - Five miles; that is the distance they are supposed to show.
8421. They do show a little further on a clear night? - Yes.


- Groves: about 5 to 7 miles,
- Gibson: 4 and 7 miles away,
- Stone: at about 5 miles distant,
- Lord: Pretty near south of us, 4 miles to the south

Lord who was the most experimented of all stated;
7120. Suppose the Titanic was 7 or 8 miles from you between 11.30 and 12 o'clock, would those on her bridge have been able to see your lights? - Easily.
Remembering that the yellow-funnel steamer Lord sighted on the southwest the next morning, beyond where this man had left, was even estimated at a mere 8 miles away!

In 1912, there was no way to establish with precision the distance of an observed vessel by her navigation lights alone. It seems that they were all using a sort of epoch rule of thumb inspired by «to show for 5 miles or to show for 2 miles» instead of had to be visible at a distance of at least 5 miles or at a distance of at least 2 miles. If only they would have had the chance to compare their rule of thumb estimations against accurate distances measured from Radar or AIS, they would confirm what I am trying to point out.

That range estimation of navigation lights is also very true today. The United States coast pilot states:
(159) The maximum distances at which lights can be seen may at times be increased by abnormal atmospheric refraction. In some conditions of the atmosphere white lights may have a reddish hue. Navigational lights should be used with caution because of the following conditions that may exist.
(164) The distance of an observer from a light cannot be estimated by its apparent intensity.
(170) Lights of equal candlepower but of different colors may be seen at different distances. This fact should be considered not only in predicting the distance at which a light can be seen, but also in identifying it.

The CCG List of Lights, Buoys and Fog Signals:
(12) Atmospheric conditions can have a considerable effect on light transmission and the visibility of lights. The distance to a light cannot be reliably estimated from its apparent brightness.

The American Practical Navigator, Bowditch:
The distance of an observer from a light cannot be estimated by its apparent intensity.

The List of Lights, Buoys and Fog Signals Luminous Range Diagram;
Intensity in candelas against range in nautical miles.

1589382073756.png


What Samuel came up with is that the incandescent light bulbs used in the electric lanterns were made of 2 filaments shining off 16 candelas each. The Fresnel glass had a magnification factor of 8.4 but an absorption lost of 10%. The sidelights had an additional filter loss of 2/5 (sidelight range ÷ masthead light range) due to the glass dye. 16 x 2 = 32 candelas or 402 lumens or the equivalence of an incandescent light bulb of 40 watts.

Masthead light intensity:
16 candelas x 2 = 32 candelas
32 candelas x [8.4 – 10% = 7.6] = 243 candelas
Visibility range = 19 miles

Sidelight intensity:
16 candelas x 2 = 32 candelas
32 candelas x [8.4 – 10% = 7.6] = 243 candelas
243 candelas x 2/5 = 97 candelas
Visibility range = 12 miles

In 1912, engineers knew well that the precision of calibration instruments would upgrade with time, thence every calculation integrated a margin of safety. To give an idea of such a margin, if you just add 2 candelas per filament or 5 watts per lantern, the masthead light range of visibility goes from 19 to 20 miles and the sidelights from 12 to 13. Notwithstanding the fact that United States Coast Pilot publication states that the maximum distance at which lights can be seen may at times be increased by abnormal atmospheric refraction; «Navigators, crew and passengers experimented a visibility rarely or never seen before. A most peculiar night. Very much refraction entered in weather log books. Witnesses stated that rockets bursting stars had color in it due to thermal inversion; a condition required for abnormal atmospheric refraction.»

To use the Luminous Range Diagram, we need to know the light intensity in candelas which was certainly not an information readily or easily accessible. Thanks Samuel for those data. The Nominal Range table given in the same publication is the maximum distance of a listed or a charted light, namely lighthouses, which can be seen when the meteorological visibility is 10 nautical miles. It does not really apply to ships navigation lights.

Geographical Range of Light Diagram:

1589382150729.png


The List of Lights, Buoys and Fog Signals or similar publications like Pilot Books, also present a Nomogram to determine the geographical range of a light. Why such coast guard publications would publish mathematical tools to determine the geographical range of a light? Just because when the visibility is unlimited, it is the most convenient tool to use. Titanic was a brand new vessel, up to highest standards and made to last. Her masthead light and sidelights lanterns were electric and her new Fresnel lens made the beam of light to focus. The weather of that moonless and pitch dark night was dead calm, dry and cold. Navigators, crew and passengers experimented a visibility rarely or never seen before.

As a result;

The minimum visibility range of Titanic navigation lights from the official Luminous Range Diagram was:
- Masthead light = 19 miles
- Sidelights = 12 miles

The maximum visibility range of Titanic navigation lights from the official Nomogram Geographical Range of a light was up to:
- Masthead light = 21 miles
- Sidelights = 17 miles

Geographical Range by calculations:
- Masthead light = 1.169 x [√(39+5) + √140] = 21½ miles
- Sidelights = 1.169 x [√(39+5) + √64] = 17 miles

Any mystery vessel with a depiction such as witnessed by Californian’s 3rd mate Charles V. Groves, located in between Lord subjective position and the Wreck location, would either sight the signaling lamp or hear the socket distress signals loud report or subsequently be swiftly identify;

«At about 11.30, I reported that vessel to Lord. I said that by her deck lights she was evidently a passenger steamer. Yes, a lot of light. There was absolutely no doubt her being a passenger steamer. Most decidedly I do believe that the passenger steamer was Titanic. The number of deck lights she was showing indicated me she was a large passenger steamer.»

Titanic masthead light was first seen from 19 to 21 nautical miles and her sidelights from 12 to 17 miles. Just far enough for the signaling lamp visible up to 10 miles to not be seen and just far enough for the socket distress signals loud report up to 13 miles to not be heard. The perfect distance apart at the very worst moment.
 

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From endnote 1 of Appendix I from my book, Strangers on the Horizon:

1 For navigation lights equipped on vessels, the nominal range used to determine their luminous range
is usually specified for a meteorological optical range condition of approximately 13 miles. (Ref:
Llana & Wisneskey, Handbook of the Nautical Rules of the Road, Annex I – Positioning and
Technical Details of Navigation Lights.) For lights listed in the US Coast Guard Light List, the
nominal range of a given light was based on a meteorological optical range condition of 10 miles. In
these lists, the range is calculated for what is called a threshold of perception which is defined as 0.2
microlux of illumination, and is approximately four times higher than a threshold of perception to
which a probability of 50% was attached. (Pierre Blaise and Paul Pétry, “Luminous Intensity and
Range of Lights,” 6th International. Conference on Lighthouses and Other Aids to Navigation,
Washington, 1960.) An illumination of 0.2 microlux is equivalent to the illumination by a star of
apparent magnitude 2.55, just a little less than the apparent brightness of the star Acrab (beta Scorpii) in
the constellation Scorpius, which easily visible to the naked eye. One-fourth that brightness, or an
illumination corresponding to a threshold of perception to which a probability of 50% was attached, is
0.05 microlux, or equivalent to a star of apparent magnitude 4.05. The dimmest objects visible with
the naked eye is typically magnitude 6.5. (University Lowbrow Astronomers Naked Eye Observer’s Guide..)
 

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