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Colours as the sun sets

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Paul Arden
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Colours as the sun sets

#1

Post by Paul Arden » Mon Jun 12, 2017 10:40 am

Hi guys,

I always thought that the reason blue features in sea trout flies is because blue is the last colour to disappear as the light goes. When I wrote the FP last night and checked this the Internet tells me the opposite. However Flavio believes it to be true. Which is it?

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Paul
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Will
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Colours as the sun sets

#2

Post by Will » Mon Jun 12, 2017 11:30 am

I think the blue thing is about how far down blue light can penetrate the water, and my understanding is that it can depend on the colour of the water.

If it's clear water/oceans then blue and green can penetrate the furthest. My copy of "What Fish See" (Kageyama) says

"As light passes deeper... light waves that are short and long are filtered out. Light deeply penetrating water becomes "one coloured". When light becomes "one coloured" in deep water, the only lure colours which remain bright are those which either match the water colour, are white, or are fluorescent colours of a longer wavelength. All other colours will turn dark!"

So in clear oceans blue and green go deepest. In green lakes only green and yellow may be visible at 30-40ft. In muddy water only orange and red may penetrate a few feet down.

Other things to think about are background colour (contrast) and colour-shifts over distance through water (influenced by water colour again).

Not sure how this applies to colour transmission at night though. Kageyama is silent on this!

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Colours as the sun sets

#3

Post by Paul Arden » Mon Jun 12, 2017 11:53 am

Thanks Will :cool:
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t.z.
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Colours as the sun sets

#4

Post by t.z. » Fri Jun 16, 2017 10:29 am

Image
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Graeme H
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Colours as the sun sets

#5

Post by Graeme H » Fri Jun 16, 2017 12:30 pm

This thread has a title that doesn't relate to your original question Paul.

The reason the light at sunset and sunrise is red is because blue light is scattered by the atmosphere. It's why the sky is blue for the rest of the day too.

As the sun sets, the sun's rays are travelling through more atmosphere so more blue light is scattered (filtered) away. What's left looks red.

That's not what's happening as light penetrates water though.

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Colours as the sun sets

#6

Post by Geenomad » Fri Jun 16, 2017 11:31 pm

Graeme H wrote:This thread has a title that doesn't relate to your original question Paul.

The reason the light at sunset and sunrise is red is because blue light is scattered by the atmosphere. It's why the sky is blue for the rest of the day too.

As the sun sets, the sun's rays are travelling through more atmosphere so more blue light is scattered (filtered) away. What's left looks red.

That's not what's happening as light penetrates water though.
All true and btw the graph T.Z posted is probably for nice clean seawater.

One more consideration, as the sun sets a change occurs in the trout's eyes - the cone cells which see colour begin to retreat and the rod cells which see shape begin to advance. At night, any colour is good as long as it is black or lumo. :)

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Colours as the sun sets

#7

Post by Paul Arden » Sat Jun 17, 2017 12:15 pm

The thread topic does relate to the original question Graeme, it's only that the answers are different. The light may appear red because the light scatters but does this mean that red colours take longer to disappear than blue ones? I see the need for a colour chart next sundown!

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Colours as the sun sets

#8

Post by Graeme H » Sat Jun 17, 2017 1:23 pm

The mechanisms are different. Red light is the first to be absorbed by water and the last to be scattered by air. (Simply put, light is stopped by water and deflected by gas.)

In air, Raleigh Scattering is the reason we get blue skies and red sunsets.

In water, light is absorbed, not scattered in the same way it is in the air. Red light is absorbed more quickly than blue in water.

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Colours as the sun sets

#9

Post by Paul Arden » Sat Jun 17, 2017 2:25 pm

Ok but I don't think any of the above answers my original thought as to which colours disapear first as the sun sets! I do remember looking at teal blue and silver once the sun has gone and detecting blue - I shall go to a paint shop and borrow a colour chart. With the moon in the jungle it's possible to see colours by the way.

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Colours as the sun sets

#10

Post by Graeme H » Sun Jun 18, 2017 12:22 am

Ah, sorry Paul. I didn't pick up that from the post. I didn't realise you were asking about the drop off of colours under the water as the sun sets. My fault ...

Since the colour of the light itself at that time of day is red and red is the first colour dropped from the spectrum in water, every object under the water gets darker more quickly than we see it above the water.

Blue objects viewed under red light look dark even above the water.

Red objects viewed under red light look comparatively brighter, but under water there is less red light to view them with, so they'll be dark too.

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Graeme
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