Absorbtion vs refraction

[Hendrix]

hi Guys, I'm not a photographer or diver- but a bass fisherman, and am currently trying to understand the relationship between light, depth, TIR etc...and using lures to catch bass. Im getting there but have one particular Q that is bugging me, and you guys might be able to help.
Why is red light the first to disappear with depth?
a quick Google suggests this is due to absorbtion, not refraction- but how can this be when red light has better penetration in say foggy air than other wavelengths? (that's why tail/fog light are red on your car )

Thanks H

 

[havnmonkey]

Actually a physics question. Different colors are just different amounts of energy expressed in wavelengths, Red is the least energetic of the visible spectrum. In other words RED is too much of a panzy to make it past 8-10 ft deep.

solid water is a much stronger barrier than fog. Water is also a great absorber of energy.

 

[donacheson]

hi Guys, I'm not a photographer or diver- but a bass fisherman, and am currently trying to understand the relationship between light, depth, TIR etc...and using lures to catch bass. Im getting there but have one particular Q that is bugging me, and you guys might be able to help.
Why is red light the first to disappear with depth?
a quick Google suggests this is due to absorbtion, not refraction- but how can this be when red light has better penetration in say foggy air than other wavelengths? (that's why tail/fog light are red on your car )

Thanks H

Speaking as a phyicist, it's a question of red light experiencing less scattering in air and small fog droplets and more absorbtion in water. Vice versa for blue. It explains why the clear sky and deep water are blue.

Don't try to understand the physics of it (I don't recall anymore); just accept what I've said as fact - if you can. <G>

 

[CompuDude]

You could also think of it in terms of wavelengths, and not be too far off. The longer wavelengths get picked off earliest. Thus, red (longest visible wavelength) hits the water molecules first, while the tinier blue (really short wavelength) slips a little farther through, past those water molecules.

 

[Jamdiver]

hi Guys, I'm not a photographer or diver- but a bass fisherman, and am currently trying to understand the relationship between light, depth, TIR etc...and using lures to catch bass. Im getting there but have one particular Q that is bugging me, and you guys might be able to help.
Why is red light the first to disappear with depth?
a quick Google suggests this is due to absorbtion, not refraction- but how can this be when red light has better penetration in say foggy air than other wavelengths? (that's why tail/fog light are red on your car )

Thanks H

Hi hendrix, I answered a question earlier on another subject that I think just might help you a little.

My post on the subject...
Relevant quote from another post.

As i'm sure you're well aware, with increasing depth underwater, sunlight is absorbed, and the amount of visible light ... the colour spectrum is rapidly altered with increasing depth.
Because absorption is greater for long wavelengths (red end of the visible spectrum) than for short wavelengths (blue end of the visible spectrum), the colour spectrum is rapidly altered with increasing depth.

 

[cirwin]

Hi,

You asked a great question, and I thought I would take a stab at the answer, since I am a physics teacher.

In a nutshell, you can think of light being made up of waves. Red light has a longer wavelength and blue light has a shorter wavelength.

In general, shorter wavelengths (blue) are scattered more (i.e. they get bounced around by air molecules, water molecules, etc.). This is why the sky is red at sunset. Since the sunlight has to travel through more atmosphere at the horizon, the blue light and even the yellow light is scattered, and only the red (long wavelength light) makes it through relatively unscathed. This is unrelated to the aborption of colors by water.

Every molecule (e.g. water) absorbs certain frequencies of light, but not others. Most of the light that water absorbs is not visible (it is actually infrared, or what we would think of as heat). Some of the absorption of water spills into the red end of the visible light spectrum, hence the drop off in red light as you descend.

Your question also mentioned refraction. Refraction is when light bends as it moves from water into air or air into water (or really any time it goes from moving in one thing to another). The net effect of this is to make a fish appear closer to the surface and farther away from your boat than it really is. For example, a bass that is really 5 feet down and 3 feet away from you might look as though it is 4 feet down and 3.5 feet away. If you have ever noticed how a straw in a glass of water looks bent at certain angles, this is the same phenomenon.

Anyhow, I hope this was helpful and not too technical!

Cheers,

Chris

 

[Hendrix]

Hi,

This is unrelated to the aborption of colors by water.


Anyhow, I hope this was helpful and not too technical!

Cheers,

Chris

Thanks Chris, and the earlier posters.
So the red light dropping off sooner in water than the other WL's, is as a result of it having a greater component of heat than say blue light.
So following on from this...water can obsorb heat more readily than air (true?) so that's why red light travels further than blue in air, but the opposite is true in water.

 

[Walter]

It has nothing to do with heat.

 

[cirwin]

Walter is right. It has nothing to do with heat. I only mentioned heat to get at the following: there are (obviously) different colors of light. What makes each color of light different is the length of the lightwave. Once the waves get too long, we can't see them anymore (same thing happens when they get too short). Think of it like sound: elephants communicate in "voices" that are so "low" that we can't hear them, and dogs can hear very high pitches that we can't. Anyhow, we are actually pretty familiar with the other types of light that we don't see. Here is a list:

Radio Waves, Microwaves, Infrared (heat), Visible Light, UV rays, X-rays, Gamma Rays

Since we call any light wave that is around 0.000000007 m in length "red," and we do not call light waves red that are any other size, red light does not have any more heat in it than it has X-rays or Blue light.

I hope this helps!

 

[Crimson Ghost]

Hi,

You asked a great question, and I thought I would take a stab at the answer, since I am a physics teacher.

In a nutshell, you can think of light being made up of waves. Red light has a longer wavelength and blue light has a shorter wavelength.

In general, shorter wavelengths (blue) are scattered more (i.e. they get bounced around by air molecules, water molecules, etc.). This is why the sky is red at sunset. Since the sunlight has to travel through more atmosphere at the horizon, the blue light and even the yellow light is scattered, and only the red (long wavelength light) makes it through relatively unscathed. This is unrelated to the aborption of colors by water.

Every molecule (e.g. water) absorbs certain frequencies of light, but not others. Most of the light that water absorbs is not visible (it is actually infrared, or what we would think of as heat). Some of the absorption of water spills into the red end of the visible light spectrum, hence the drop off in red light as you descend.

Your question also mentioned refraction. Refraction is when light bends as it moves from water into air or air into water (or really any time it goes from moving in one thing to another). The net effect of this is to make a fish appear closer to the surface and farther away from your boat than it really is. For example, a bass that is really 5 feet down and 3 feet away from you might look as though it is 4 feet down and 3.5 feet away. If you have ever noticed how a straw in a glass of water looks bent at certain angles, this is the same phenomenon.

Anyhow, I hope this was helpful and not too technical!

Cheers,

Chris

Chris - -

Great post – but you got me thinking….I am just sitting here drinking the morning coffee thinking about getting my butt to work….oh well.

I always understood the concept of wave lengths – red being the longest visible and violet being the shortest visible. If the sky is red at night because it takes the longer wave length to travel the atmosphere where the shorter why can we see a burst of green for a second at sunset (yes, on rare occasions). I personally have never witnessed this, but recall people speaking of it. I figure if green can be seen than theoretically shouldn’t red, orange and yellow also be seen? I have a 7 year old inquisitive son (and an oblivious 5 year old daughter for that matter) – but the boy asks me all the time about the different colors he can see in the sky and also about refracted light (rainbows from my fish tank mostly), I like to be able to answer him correctly and of course offer more than he needs