Naked Science Forum
General Science => General Science => Topic started by: DoctorBeaver on 26/08/2009 23:38:39
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and other lighthouse based questions:
What is the power output of a lighthouse compared to a 100w household bulb?
Are lighthouse lights just bigger versions of household bulbs?
Do lighthouses still perform a useful function in these days of GPS?
Any pharologists who can answer these questions will have the beaver's eternal gratitude.
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Some modern lighthouses have 1 million candle power, a standard 100 Watt incandescent bulb has approximately 100.
Lighthouse keepers must have been bored out of their minds ... [:)]
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Some modern lighthouses have 1 million candle power, a standard 100 Watt incandescent bulb has approximately 100.
I wonder if they will try and replace it with energy-saving bulbs...
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Some modern lighthouses have 1 million candle power, a standard 100 Watt incandescent bulb has approximately 100.
I wonder if they will try and replace it with energy-saving bulbs...
Replace them all with LEDs. It would be a shame to tear down that bit of history.
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Lighthouses don't just use a bulb. They use a reflector and a large, stepped, lens - called a Fresnel lens, to use as much of the lamp output as possible and beam it in the wanted direction. The whole arrangement rotates at a specified rate (different for each particular lighthouse and with multiple beams, sometimes and has shutters, often with coloured filters to limit the directions in which the beam actually points and to give mariners information about their bearing from the light. Red and green sectors are often used to keep you the correct side of the light or to direct you to a navigable channel.
Modern lamps have powers of several kW but the optical arrangement increases the effective light level by a factor of tens of times. The lamp envelopes used to be enormous but new lights use high intensity gas discharge (energy efficient and better for the optics, being more of a 'point source'). There was a time when Carbon Arcs were used, apparently but they were a nightmare to keep running. I remember playing with a carbon arc lamp in an old cinema projector and it was not reliable. And, of course, reliability is pretty essential for ships out there on a dark and stormy night and there is a spare, which is automatically brought into use when the main one fails.
Small lights may be only a matter of a few watts.
I visited the Start Point light last year and was given a tour by a nice elderly gent who showed us 'the works'.
I remember that I learned to smoke when I was about 9, standing at the top of Smeaton's Tower, on Plymouth Hoe, way back when (entrance fee was about 2d, if I remember right). I never took it up though - nasty habit for all concerned but I did feel cool up there!
"Did you know" that they have a blind which is deployed during the day so the Sun doesn't get focused onto the lamp works and damage it?
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I know it's not true but that doesn't make it less funny...
Believe it or not...this is the transcript of an actual radio conversation between a US naval ship and Canadian authorities off the coast of Newfoundland in October 1995. The Radio conversation was released by the Chief of Naval Operations on Oct. 10, 1995.
US Ship: Please divert your course 0.5 degrees to the south to avoid a collision.
CND reply: Recommend you divert your course 15 degrees to the South to avoid a collision.
US Ship: This is the Captain of a US Navy Ship. I say again, divert your course.
CND reply: No. I say again, you divert YOUR course!
US Ship: THIS IS THE AIRCRAFT CARRIER USS CORAL SEA*, WE ARE A LARGE WARSHIP OF THE US NAVY. DIVERT YOUR COURSE NOW!!
CND reply: This is a lighthouse. Your call.
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I know it's not true but that doesn't make it less funny...
It's not? They would have had me fooled then
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Too funny to be true.
I bet that US Navy Captain suddenly had a lot of things to look to [:D]
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Left hand down a bit.
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Apparently it has now been admitted that the aforementioned interchange between the naval ship & the lighthouse did happen.
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Thank you all for your replies, by the way.
I notice that no-one has addressed the question of GPS. Surely, GPS is now accurate enough to keep ships away from rocks etc. so are the days of the lighthouse numbered?
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afaik the days of GPS are numbered too!
Don't turn the lights out just yet.
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SC - why do you say that?
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http://www.guardian.co.uk/technology/2009/may/19/gps-close-to-breakdown (http://www.guardian.co.uk/technology/2009/may/19/gps-close-to-breakdown)
I read this some while ago. Worrying, isn't it?
I'll have to learn to read charts properly again!
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That was an interesting report, SC. It shows the effects of the economic situation at play in the US, but it would really be out of the question for the US to let the GPS system fail. Besides the more or less total dependence that commercial land, sea and air traffic has on it, many important US weaponry uses it for precise targetting. Given the investment in that field, the cost of GPS is negligible. Anyway, as the article says, there is the European, Russian, Chinese and Indian systems to use instead and modern navigation systems are starting to have to be multi-system capable which should give lots of options.
On the subject of lighthouses, I sailed around the Isle of Wight last weekend and noted that for both St Catherine's Point and The Needles lighthouses, the lights keep rotating even when the light is off (in daytime). The sun was in such a position that the reflected on/off pattern could well have been the same as what it would be at night (I didn't check with the charts), but that was surprising in itself; in fact at first I thought that the light was still operating. Do you know why they keep the rotation going? I would suppose the answer is that the power needed is negligible and there may be more problems with stopping and starting that with continuous use. Do they still float the whole assembly of mercury?
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Yes, interesting report. Thank you, SC.
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A not very bright light house !
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That not-so-bright light house could certainly use some TNS knowledge.
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graham.d
It may be that it's better to keep it rotating to avoid it settling into a distorted shape - or to stop the bearings getting stuck. After all, it's a pretty vital bit of movement.
I know that big horizontal shafts are rotated to stop them sagging. e.g high power generator sets and aero turbines.
Or it could be an alternative way of stopping the Sun's being focused on one spot.
I don't really believe that GPS could ever be turned off but the Guardian, even if their typesetting may not be what it might be, is not often wrong.
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Regarding the GPS, two thoughts come to mind. On the satellite end - a solar flare could disrupt the signals http://www.news.cornell.edu/stories/Sept06/solar.flares.gps.TO.html (http://www.news.cornell.edu/stories/Sept06/solar.flares.gps.TO.html).
On the vessel end, GPS's break, and batteries die (especially aboard blow-boats [:o]). I knew a person who was racing the Annapolis to Newport race several years ago and lost all his electronics to a lightning strike at the mouth of the Chesapeake - thankfully, he remembered his celestial nav and managed to win the race with a chart, sextant, and parallel rules.
I never go out without a chart and Weems protractor, even though the creeks and rivers of the lower Chesapeake are shallow, the bottom is forgiving, as long as one doesn't run aground on dead high tide.
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Speaking of sailors.. did you know that 3.14 of all sailors are pirates?
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Ah-Haar who told ye that?
No grasp of sadistics 3.14:1 sounds like raidng party odds!
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Speaking of sailors.. did you know that 3.14 of all sailors are pirates?
38.62% of pirates are Black Sabbath fans.
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You`re just paranoid!
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You`re just paranoid!
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fbestsmileys.com%2Flol%2F4.gif&hash=dc0017defb1737ae43c0ff6efcb35b2a)
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should I have said pi-rates?
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Coquina.rocks, I note that the article suggests that it is the receivers, not the satellites, that can be temporarily disrupted by solar flares. It seems to suggest a reduction in signal level (probably due to ionisation in the upper atmosphere) is responsible. I think this problem is of fairly short duration, will only affect some receivers, and would be likely to cause a reduction in the number of satellites "visible" to a paticular receiver. This is not good, especially for vehicles needing navigational updates on a regular, fast basis, but would be less of a problem for yachts [blow-boats indeed :-)]. I don't know anyone who sails offshore regularly who does not always take charts and traditional nav aids and, personally, I always have the right chart on the chart table at all times. I also have 2 GPS systems in use at all times so a discrepency will indicate that the results may not be reliable. I have seen problems too. Sailing off Greece last year one GPS was giving plausible but incorrect readings - about a mile out of position. I think the system had somehow lost its datum.
There are some GPS "black spots" too where, despite the number of satellites zipping about, the coverage can be insufficient to get good position at all times. I would suppose when all the national systems are on-line, and multi-system receivers are available, the potential problems and likely failures will be less. But then, if all the electronics gets zapped by lightning, it's a good idea to have traditional methods at hand.
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A not very bright light house !
And what causes you to answer, in a misguided belief the poser of this question is brighter than the cabbage?
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I think I may have just been insulted [???]
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Sailing off Greece last year one GPS was giving plausible but incorrect readings - about a mile out of position. I think the system had somehow lost its datum.
graham.d
Have you come across the problem of display format?
It can show you degrees/minutes/seconds or degrees/minutes/decimal monutes.
I spend a good while trying to reconcile two, contradicting, hand helds, one time. The guy I was with had really had his confidence in GPS shattered until I sussed out the prob.
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No. All the GPS units I have used display decimal minutes, but I think I would have spotted a second (") symbol had it been displayed. In any case, it was the plotter that was out. Around the Ionian Islands the datum has quite an offset. Although the charts are reasonably relatively accurate (apart from the odd unmarked rock) they are out quite a bit from absolute position. When you first switch on, the GPS can easily tell you that you are moored a mile or so inland. You have to set an ofset on the datum to correct this. Once entered it should maintain this. However I can only think that something caused the GPS system to forget this offset. Switching off then on again seemed to fix it, which points to some error in the plotter. You don't really need any electronic aids in the Ionian but it was disturbing to see that the plotter did not agree with reality. Checking with a handheld confirmed that reality was correct and the plotter was out :-)
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There's a lesson for us all then.
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Perhaps the difference in is in the mapping datum used for Ordinance Survey maps and naval charts. These are often NOT the same as the datums the handheld unit have loaded in them nor are the necessarily are they corrected for the GPS system itself. In North America two sets of datum are used - NAD27 & NAD83. The NAD27 is based in the Clarke Elipsoid, the NAD83 is base on the GRS80 ellipsoid. Neither of the ellipsoid that attempt to approximate the earths surface are very good for mapping locally. The GPS signal must be interpreted with respect to the local datum used and this WILL in many case vary from the 1936 Ordnance Survey maps, which I believe were based on the Clarke Ellipsoid (That needs to be verified)
The WGS 84 datum used for navigation is 5.31 arc seconds off of the Prime Meridian at Greenwich and is not the same as either the 1936 Ordinace Survey or the NAD27
The GPS Unit must be set up withe the correct map datun for the maps and charts used. Otherwise there will be an observable difference in locations given.
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JimBo,
Does them nads have anything to do with yer gonads? Heard that ol' mule o' yours did a number on yours the other day.
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JimBob, I agree you have to set the correct datum for the chart. The point is that the plotter maybe forgot the datum. I did set it and it was OK when I started out, at some point lost its mind (though gave out a plausible position), and then only recovered following being power cycled.
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JimBob, I agree you have to set the correct datum for the chart. The point is that the plotter maybe forgot the datum. I did set it and it was OK when I started out, at some point lost its mind (though gave out a plausible position), and then only recovered following being power cycled.
Sounds as if the OS was written by Microsoft!
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JimBo,
Does them nads have anything to do with yer gonads? Heard that ol' mule o' yours did a number on yours the other day.
naw. frethak got that kick i I use a mule cup