How bright are lighthouse lights?

DoctorBeaver · « **on:** 26/08/2009 23:38:39 »

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.

RD · « **Reply #1 on:** 27/08/2009 05:49:59 »

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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Variola · « **Reply #2 on:** 27/08/2009 08:55:03 »

Quote from: RD on 27/08/2009 05:49:59

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...

DrChemistry · « **Reply #3 on:** 27/08/2009 09:10:37 »

Quote from: Variola on 27/08/2009 08:55:03

Quote from: RD on 27/08/2009 05:49:59
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.

lyner · « **Reply #4 on:** 27/08/2009 10:57:31 »

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?

JnA · « **Reply #5 on:** 27/08/2009 11:01:57 »

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.

Chemistry4me · « **Reply #6 on:** 27/08/2009 11:16:41 »

Quote from: JnA on 27/08/2009 11:01:57

I know it's not true but that doesn't make it less funny...

It's not? They would have had me fooled then

DrChemistry · « **Reply #7 on:** 27/08/2009 11:20:03 »

Too funny to be true.

I bet that US Navy Captain suddenly had a lot of things to look to [

]

lyner · « **Reply #8 on:** 27/08/2009 18:46:45 »

Left hand down a bit.

DoctorBeaver · « **Reply #9 on:** 28/08/2009 11:23:09 »

Apparently it has now been admitted that the aforementioned interchange between the naval ship & the lighthouse did happen.

DoctorBeaver · « **Reply #10 on:** 28/08/2009 11:25:26 »

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?

lyner · « **Reply #11 on:** 28/08/2009 13:59:47 »

afaik the days of GPS are numbered too!
Don't turn the lights out just yet.

DoctorBeaver · « **Reply #12 on:** 28/08/2009 14:57:08 »

SC - why do you say that?

lyner · « **Reply #13 on:** 28/08/2009 16:54:34 »

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!

graham.d · « **Reply #14 on:** 28/08/2009 18:32:37 »

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?

DoctorBeaver · « **Reply #15 on:** 28/08/2009 19:22:26 »

Yes, interesting report. Thank you, SC.

neilep · « **Reply #16 on:** 28/08/2009 21:30:05 »

.

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A not very bright light house !

DrChemistry · « **Reply #17 on:** 28/08/2009 22:09:15 »

That not-so-bright light house could certainly use some TNS knowledge.

lyner · « **Reply #18 on:** 28/08/2009 22:50:09 »

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.

coquina.rocks · « **Reply #19 on:** 29/08/2009 00:22:04 »

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 [nofollow].

On the vessel end, GPS's break, and batteries die (especially aboard blow-boats [

]). 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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How bright are lighthouse lights?

DoctorBeaver (OP)

lyner

lyner

DoctorBeaver (OP)

DoctorBeaver (OP)

lyner

DoctorBeaver (OP)

lyner

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