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Bernard
posted : March 3, 2007 Post subject: fluorescent colours
Excuse me butting in on your forum - I am an angler researching the response of trout to colour.
Since short wave light penetrates most deeply into water, I assume this includes uv light and not only the visible blue. Does this mean that red and yellow fluorescent paints are visible in colour at depths beyond penetration of long wave light, i.e. where regular orange and red are not visible in colour? Obviously I am only interested in situations where there is no 'contamination' from artificial light sources.
I would be grateful for an answer that is based on direct experience.

 
ADM Diving
posted : March 3, 2007 Post subject: fluorescent colours
Hi Bernard, I answer the technical forum Q&A's here - what you pose is an interesting question.

Well spotted about the long wavelengths - as a rough rule of thumb each spectral component in the visible spectrum is absorbed at a rate of about a colour every 8m of depth - so at 24m all the red is gone, orange and yellow. Most things we buy and use, are never photochromically exact in wavelength. Most items are a blend of colours and appear as a tan or dull colour at depth below the main components spectral cutoff... Ie Red blood looks a green algae like materail coming from a wound below 16m...

If you want to look up the physics of this - start with the applied physics branch that looks at Emissivity. This will help you see the absorbtion and reflection (and translucent properties of paints and materials to specific Electromagnetic radiation - albeit we call one area of this light).

So to answer your question it depends on how good the quality of the paint is - and how photochromically narrow the paint is - if it is narrow and only reflecting its own dominant wavelength or colour then it will go progressively black below the floor of that colour... i.e pure red things will go black by the time orange floor is reached at circa 16m.

Most flourescent paints and colours are energetically favourable to its own light (usually UV) and gives off a bright or enhanced colour (emessivity - energy functions of black body radiators explains). So given flourescent colours only favour their light wavelength it is incombent that they do appear to have a brighter colour at depths below the natural colour base i.e. yellow flourescent looks an off yellow at 40m when yellow is normally dead below 24m.

This is why our diving trapeezes we manufacture use special braids/ropes that contain flourescent properties so that ropes are all very visible - even more so when a low power light is shone in their general direction...

A nice question.. if you want the detailed physics and applied mathematics behind all this - then email me direct on mail@admdiving.co.uk

cheers Andrew.

 
ADM Diving
posted : March 4, 2007 Post subject: fluorescent colours
Hi Bernard,

No worries it is a very fascinating subject as the refractive properties and indeed visibility is both affected on the horizontal plane and vertical plane in water in very different ways. Also is the ability of Fish to ‘perceive’ such differences – Ichthyologists have long established the eye’s of fish don’t have the same structures as we and other mammals have (rods for light or intensity – often dumbed down to be the Black & White receptors, and Cones for the primary colour receptors – although in most mammals they sort of do it like photo copiers and colour laser printers and use offset hues and not R/Y/G)

The differences between absorption depths in sea and fresh water is pretty much the same, what affects it greatly in sea water is effects called Haloclines which is formed when fresh water runs into the sea. Halocline = salinity layering. In both Fresh and Sea water Thermoclines tend to have similar effects such a Haloclines. Thermocline = temperature layering.

Suspended Material just acts like a graded filter, so it is occluding all light by a given % proportional to the volume of suspended material or another way of looking at it is that it is reducing the intensity of all wavelengths by x%.

Peat and other soils that are washed down streams into lakes and other water masses, do have a disproportional effect on the wavelengths penetrated to their respective depths. These waters tend to be more devoid of light (all wavelengths) below the Red depths (8m), again generalising this is proportional the volume of suspended matter from such soils. Oh light can go to zero visibility very easily in such influxes.

So it is fair to say tannins (C76H52O46), and other compounds from Peat, soils and plant decay that colour water will kill fluorescence very near the surface (proportional to its concentration).

If your after solutions that work in stained water then the answer is to go for super fluorescence such that the much reduced short wavelengths will cause fluorescence… take care not to get into the realm of paints and solutions that are hence radioactive. (Remember the old BT Trimfone – that little dial that glowed was down to a low yield radioactive gas in a glass tube). Personally I would build your lures etc with LED’s and use the salt water as a battery for them… hence generating your own light at any depth…

Hope this further helps,

Best Regards,
Andrew.

 
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