I haven't waded yet thru all of the postings, but an early one that claimed a candle could be detected
by human eyes at a distance of 30 miles was challenged (actually, ridiculed) by Gary LaPook, who rambled on
and on using govt regulations for ship lighting and how far they would have to be seen, etc. What Gary didn't know is that scientists at Columbia University way bck in 1941 determined that a fickering candle could be seen under excellent sighting conditions as far as 30 miles away by human eyes. LaPook's big mistake was in assuming that govt requirements for ship light visibility was in any way a claim as to how far those lights could actually be seen under ideal sighting conditions - sighting conditions can vary enormously and ship's lights must assume that sighting conditions are often less than ideal.
Reference :
http://www.livescience.com/33895-human-eye.html
Also I found data concerning visibility of a 100 watt lightbulb under excellent viewing conditions - 118 km or
over 60 miles. http://sbp.so/firefly
I also found several references to instances in which relatively small freighters could easily be seen at distances of 10 miles and beyond at night, even from the deck of a ship. One such was the California during the night the Titantic sank.
One other thing I should have pointed out - it's good to see a new visitor here bothering to look back through old posts to get up to speed, Kent.
I gather the post you were referring to was
this one. Yes, my friend Gary can be quite an advocate for a certain point of view, and can provide arduous detail from the most arcane sources at some length, I well understand. He also, often enough IMO, reminds the reader to be careful about applying ideal notions to theorum.
Again, regulatory 'stuff' is an assuring box for things to be made to fit in to assure a certain level of performance under reasonably predictable conditions. And I am reminded that the regulation for ships' lights is based on the atmospheric clarity being 13 NM - which doesn't consider the exceptional case. Mothership Earth's ECS (Environmental Control System) brings the price of sight-limiting atmosphere - a couple of miles or so of dense air such that the range of light is much more limited, and moreso when her stew of vapor is stirred, settled and restirred at sea, etc.
The 'rule' -
Title 33: Navigation and Navigable Waters
------------------------------------------------------------------------------------------
PART 84—ANNEX I: POSITIONING AND TECHNICAL DETAILS OF LIGHTS AND SHAPES
§ 84.15 Intensity of lights.
K is atmospheric transmissivity. For prescribed lights the value of K shall be 0.8, corresponding to a meteorological visibility of approximately 13 nautical miles.
Maritime rule...-----------------------------------------------------------------------
If you go into that morass of detail, notice that while the given standard for visibility is 13 NM
(ref: atmospheric transmissivity, value of "K" as shown under a)), the 12 candle light is only visible for 3 NM
(see third line in table 84.15(B) in the rule). Consider then, if the existing visibility is less than 13 NM the effective visual range will be accordingly further restricted even though 'visibility' exceeds the light's range
(the more dense the infering atmospheric stuff the more attenuation, and therefore the less resulting effective visibility). And, no matter the intensity of the light, it will always be limited by the maximum visibily.
For illustration, from how far away can one really see a light house with a powerful beam on a foggy day? I'm reminded that on the sea visibility rarely exceeds 25 NM. The Navy Climatic Atlas suggests that in the vicinity of Howland island in July one should expect visibility of less than 25 NM 70% of the time, less than 20 NM 60%, and less than 15 NM 50% and less than 10 NM 39% of the time, etc. It is likely that conditions would be similar near Nauru. To Gary's credit, consider the effects of that reality on low-intensity lighting. Not saying Earhart didn't see either of the ships - but to be sure, it isn't a shoo-in.
All of that is for illustration - and hopefully that we might appreciate that perfect conditions aren't likely to be found at the sea's surface very often. But we're also not talking about sea-level observations where Earhart's view is concerned, of course, so not we're not having to strictly consider the low-level lateral
or forward visibility case.
We may view it downward, through the soup from an airplane, so the low-level conditions that provide that expectation aren't the same -
IF the intervening atmospheric interference is less vertically than would be laterally at the surface. And again, it is worth noting for mental sobriety that sea conditions are not likely to be ideal for spotting distant low-intensity lighting.
And again, we do also have Earhart's reports of having seen something, so apparently something was seen - what would it have been? I tend to favor a ship
(she said as much) - but I recognize the potential peril of that assumption, largely thanks to Gary.
So what could she have seen?
The application of lumens to assure visibility may be of some interest in considiering that for an answer, that's all. If these points are worthy, more information exists regarding the requirements for lights on aircraft, which are also very carefully spelled out (atmospheric interference exists at altitude as well). Notice that position lights must be 40 candles, see (and if that's more regulatory drivel than one cares for, skip it - Earhart DID say she saw something):
Regs on light...More regs on light...Still more......and more...Notably, the anti-collision light which must be 400 candles -
Anti-collision...Fairly stiff candella requirements for a reason: intent to be seen in time to avoid collision with relatively fast moving craft aloft. Do they tell us much about how restricted the view of a dimly-lit ship might be from aloft? They suggest something about atmospheric impedance - but not fully enough to preclude the view a pilot might have of a ship with well-enough attuned night vision, IMO.Of course these provisions are meant to ensure a certain level of visibility by deliberately overcoming, to some important degree, the impediments of atmospheric conditions, etc. as we've considered them. Ultimately they too
can be quite limited - but I often see airplanes many miles away in my southern, somewhat typically hazy skies...
---
The two references you provided are interesting, but they are also theoretical computations. The first one appears to be based on extrapolation from a laboratory experiment which appears to make no allowance for clarity of the air. It was also based on light of (blue-green) wavelength of 510 nanometers, to which the human eye is most sensitive. These are somewhat ideal - and of course they would be for the sake of what they did. Point being, they have limited value in the real world.
And once more, I'm not saying Earhart didn't see the lights of either the Myrtlebank or the Ontario - but
with a nod to Gary's professorial wonderment, one might wonder, did either have lights happening to be of a wavelength of 510 nanometers? Joshing a bit - the point is conditions were not likely ideal, and I won't swat away the question 'were their lights intense enough for this to have been probable'? I don't really know; I do know Earhart apparently saw something that may well have been at least one of the ships. But I will throw in, again, that I appreciate Gary's insightful analysis (yes, I confess, he largely gave me the bug for digging into this kind of stuff...).
Here's a bit of info on the human eye in this regard, here,and,
here.It doesn't appear by what I've seen so far that anyone ever went out into the desert or to sea to fully validate the 30 mile range of a candle as theorized (or for one thing it likely would have been mentioned in the article). Had they sent someone to the top of a mountain with a candle and to then have test subjects press a button when the guy on the mountain moves a shutter away from in front of the flame such that the correspondence of the button pushes with the timing of the flashes would tell all, we'd have more useful information, IMO. I'd bet one could count on 30 miles of single-candle range on the moon - but with no air to attenuate the light we also lack the ability to keep a candle lit in that place...
So could Earhart have seen either of the ships, or other lights? I still believe she could have, but I can't be certain as to from how far away, or what they were.
Having reviewed a bit more background as of this morning (you'll notice I've edited this lengthy post somewhat to add some clarity) I am reminded of some clarifying points Ric Gillespie once posted - "ship in sight ahead" was reportedly uttered by Earhart herself at 1030Z.
It is also noted therein that Nauru had a light - a sometimes tempting alternate to 'ship' I suppose - one "New Nauru fixed light latitude 0.32 S / longitude 166.56 E five thousand candlepower 560 ft above sea level visible from ships to naked eye at 34 miles" (and note that at an altitude of 560 feet and 5,000 candlepower, it exceeds the 30 mile single candella presumption by only 4 miles...).Out of all that stew I have to come to some level of confidence (high or low is reader's choice) based on the web of her likely proximity at the time of the report and what I believe is reasonable to assume about the ship's lights, etc. I also have to give her raw report some credence, as other than being a complete klutz when it came to the radios, she was pretty smart and observant and an experienced aviator.
She said she saw a ship; she may well have, despite the odds, seen a ship. I realize that after all the detailed analysis, that is a bit mushy of me, but it's a mushy world with a very large Pacific Ocean.
Speaking of which, I can see 'taking that' two ways (the size of the dark Pacific that night) -
'the lights coulda been anything', or 'what else could it have been'... - a point of view thing, perhaps. Given the light attenuation possiblities we face, a good corollary might be 'she must have been very close to have seen that after all'.
Glad to see you reading old stuff and digesting and thinking - thanks for that.
Details added for clarity 5/29/2014.