Green Lighthouses not Looming

[earlybird]

According to "The Guardian" here

 

[johnalison]

I can't say that I understand the physics of this. Loom must be due to scattering in the atmosphere, and I see no reason why this should not be identical for any given wavelength and intensity. Maybe what people are complaining about is the speed of the flash starting and stopping, which would be instantaneous with an LED as opposed to the pleasing phasing of a traditional rotating light. My guess is that the journalist got the wrong end of the boathook.

 

[Stemar]

My guess is that the journalist got the wrong end of the boathook.

Well, what a surprise...

 

[Bunbury]

Is it not the replacement of the rotating lenses rather than changing the light bulb which will stop the 'looming'?

 

[LittleSister]

Rage against the dimming light: Irish rebel over lighthouse LED makeover

 

[johnalison]

Is it not the replacement of the rotating lenses rather than changing the light bulb which will stop the 'looming'?

I think that is part of the problem but I imagine that older systems didn't have a sharp cut-off or that there was a sideways 'loom' that preceded and followed periods of illumination, softening the effect. There is something restful about a traditional light flashing in the distance when seen from land. I can imagine that an LED switching on and off could be very irritating in comparison.

 

[LittleSister]

It's not clear the writer knew what they were talking about.

I had initially assumed, because they were talking about doing away with the mercury used to support the rotating lens, that they would simply be flashing the relevant signal, so no rotating beam, but there's a reference to a mechanical bearing.

 

[LittleSister]

Hadn't spotted that there was already a thread about this:
Green Lighthouses not Looming

 

[westhinder]

. My guess is that the journalist got the wrong end of the boathook.

Could it be that the journalist has correctly represented the views of a campaigner who got the wrong end of the boathook?
That is my impression of the article. I will confess I’m a journalist myself, so I cannot rule out a certain bias ?

 

[HissyFit]

I suspect that the campaigners haven't switched to low energy lightbulbs in their homes, worrying about the loss of light. They obviously haven't cottoned on to the fact that incandescent bulbs waste the greater part of the energy they use as heat. Low energy doesn't mean low light; it just means the same light level can be produced without the same amount of heat dissipation. I thought everyone was made aware of this before the sale of incandescents was banned. Obviously not everyone was paying attention. Sorry for the egg sucking lecture.

 

[halcyon]

Could it be that the journalist has correctly represented the views of a campaigner who got the wrong end of the boathook?
That is my impression of the article. I will confess I’m a journalist myself, so I cannot rule out a certain bias ?

A bit I heard on the radio the other day, it refers to the old light being visible before the lighthouse, the LED is only visible when the lighthouse is in direct line of sight, so closer to shore / danger.

Brian

 

[Slowboat35]

I can't say that I understand the physics of this. Loom must be due to scattering in the atmosphere, and I see no reason why this should not be identical for any given wavelength and intensity. Maybe what people are complaining about is the speed of the flash starting and stopping, which would be instantaneous with an LED as opposed to the pleasing phasing of a traditional rotating light. My guess is that the journalist got the wrong end of the boathook.

However if the new light is to be of a blue-white colour then the same wavelength of light is not being applied and may well make a difference to atmospheric scattering.
I also suspect as others have mentioned that the cutoffs of the LED lights will be much sharper and that too would modify scattering efects compared to a traditional lamp.
For a start why not make the light the same 'colour' as the old ones - that harsh LED blue-white is hard on the eyes.

And in spite of this 'advance' in technology the poor weedy little LEDs, despitebtheir eye watering dazzle can only achieve a fraction of the range (ie light intensity) the old light had. Just as every reader with a book under LEDs knows. And that's progress?

As for the idiotic argument about mecury and H & S... who the heck is in a lighthouse to be affected by it? Or do they see the considerable value of all that mercury as a revenue stream?

 

[Deleted member 36384]

The loom was always useful for establishing a reference point to wait for the light to rise. Interesting observations on testing the differences between incandescent and LED light through a Fresnel lens.

Implementation and Test of a LED-Based Lamp for a Lighthouse

... The new LED source illuminance on the inner surface of the Fresnel lens results, as average value, 68.8% of the illumination obtained with the incandescent lamp. This illuminance percentage is in excellent agreement with the evaluations performed starting from laboratory measurements ...

 

[johnalison]

My impression is that an LED white light is bluer than traditional lights, hence the need for 'warm' lights. Since blue light scatters more than warmer wavelengths, this can't be the cause of lack of loom. The reduction in intensity would seem to be significant, though there is one comment that seems to suggest that the range at sea is the same as the traditional light. The complaints from those on land appear to be unexplained.

 

[sailor211]

When visiting Portland Bill light pre change to LED the guide was saying that paper of the change was to reduce the light. A deliberate decision, lights being less important in the days of electronic navigation.

I also recall an article that ships come closer to see the light thus confirming the position.

Both statements would seam reasonable.

Now Portland Bill is LEDdose the characteristic still change as you go north ?

 

[black mercury]

Having travelled down the North Channel into the Irish Sea to the Isle of Man over the years it was obviously clear where the Copeland lighthouse was. It's loom could be seen for many miles casting it's light into the sky below the horizon. Then they swapped it for an LED a few years ago. The light is now best described as pathetic compared to the incandescent bulb. I am all for reducing energy, but I didn't think the incandescent lighthouse bulbs were that high a wattage, all done through the lens. The range was reduced by only a few miles but you need to be really looking for the light. What you see now is a flashing dot. It is that bad they now have a permanent white light to help you find where to look.
I have said before about LED nav lights on small boats at the extreme of their range not being as visable as incandescent lights, but I was basically told I was talking nonsense on here. But I see what I see. Maybe my eyes are different than other people's but incandescent nav lights, at a greater distance, give off a kind of glint effect that catches you eyes, LEDs don't at the same distance. All you see are coloured dots. LED lights on channel markers or cardinal marks etc seem OK, but they are seen relatively close. Maybe someone on here can explain this scientifically, but I do know incandescent light has a wider wave band than LED light

 

[ltcom]

Either the journo or the source could be wrong was my thinking too. Leds can be brighter than incandescents. They can be pulsed. Capacitors and ic chips stuck in the mix can make them fade rather than be on or off i imagine.
I would have said non story if not for a poster saying they have witnessed it but then whoever made the circuit could have done it by design.
An led lighthouse could be brighter or dimmer depending upon design of circuit. Colour could be matched easily.
I would say the less of loom is wrong (the physics state that as johnalison points out i think although physics not my strong point) and perhaps the one witnessed by a forumite was designed that way or designed badly. Leds are great.
As long as mercury stays put (as it should in such a structure why go to the expense and potential health hazard of changing it ...... need a lot of PPE to change that stuff) ........unless some benefits of new mechanism over mercury. If it aint broke leave it alone as far as the mercury goes.
Of course if we really want to know we should ask Trinity house perhaps?
The leds......... still think it is a non story.
Rider ... .All above has been a knee jerk resonse without indepth thought so happy to be corrected politely. Correct me without being polite if like but i will attempt to not respond to those ones as it is such a lovely day to day.
Crux...... leds totally rock !!! So do lighthouses sitting upon their rocks (often but not always .......... sometimes clifftops etc)

 

[ltcom]

Whilst searching for trinity house info found this which was quite interesting on itsown imho
Lighthouses and Sector Lights - Hydrosphere
Trinity House completes Berry Head Lighthouse update
Sark Lighthouse re-engineering completed
Trinity House completes re-engineering of Start Point Lighthouse
I will attempt to contact Trinity House via email coz I found this topic interesting.