LED vs Q-Beam

Just a WAG: the light source is distributed over a larger area, reducing the breaking up effects of reflections.

It might be the difference between a spot light and a flood light. Flood lights spread their lumens over a wide area, whereas spot lights are designed to throw a tight beam over a longer distance. The LED optics might make them spot lights.

Some colors penetrate further into water than others (less attenuation), but you didn't mention there being any obvious color difference.

You make a good point. the customer never told me whether they were SPOT or FLOOD and never mentioned a color.

Color temperature plays a huge part in seeing underwater.

Look around at some of the diving sites on the internet. There is a plethora of information about color temperature and it's effects on seeing underwater. A lot of it is perception, so tailoring a setup is key.

LIDAR at specific color frequency can penetrate many feet of water. It is used for survey work from planes.

Most "white" leds are actually a blue led with a phosphorus coating over it, so it looks white while on. That is why many "white" leds appear to have a slight dirty blue tint to them. The ocean is also blue. Not sure if this is why it appears to penetrate further or not.

LIDAR is actually laser and uses green as the specific color but the point being a tight spectrum emission combined with a particular color has far greater water penetration power.

Regarding the original posters situation I would suggest using underwater LED for viewing trawl nets at night. These LED are sold for boats as a novelty feature but has practical applications as well.

This was in murky, fresh water in the Missouri River.

Were the LEDS under the water? That would account for a big difference if older light was out of the water.

No, they were inside and on top of a railing in the boat.

netmaker:

If color is matching with the scattering color of particle size in water then you will also see intense scattering as illumination in particulate matter. However, for other colors, beam will only illuminate larger objects like fish and divers and beam will remain invisible or of low visibility for the dirty water with least interference.

LED have intense color bands while arc lamps have continuous spectrum.

Thank you. That makes sense to me.

Welcome.

"If color is matching with the scattering color of particle size in water then you will also see intense scattering as illumination in particulate matter."

"LED have intense color bands while arc lamps have continuous spectrum."

Yes, but as a continuous-spectrum source includes the color (wavelength, more specifically, as 'color' is a subjective measure) which those same particles scatter, then you will still have backscatter at that wavelength whilst all the other wavelengths pass through with the result that the water will still appear murky, only monochromatically so.

As it is highly unlikely that the particles are all of uniform size, reflecting only one wavelength, you will have broad range of backscattered wavelengths, the dominate wavelength corresponding to the color of the water as seen in daylight. If the backscatter were monochromatic, as you suggest, then the backscattered light will be a pure, saturated color. This is obviously not the case with murky water anywhere in the world and so the backscatter cannot be monochromatic. The backscatter is broadband and because it is broadband, there will be backscatter regardless of the source type, ie, the water will appear murky in both cases.

I strongly suspect that the primary difference in visibility here is due far more to the geomtrey of the respective beams than to spectral differences.

I might also point out that white LEDs have a broadband emission as well. How to tell? Color rendition.

Even though white LEDs are dominant in the yellow and blue (blue LED + yellow phosphor), you can see reds all the way through violet (violet, as the 'blue' component is rather broad and includes wavelengths in the violet). If on the other hand white LEDs emitted only some combination of narrowband blue and yellow, those would be combinations of colors you would see in white-LED light, but it isn't; you see the full spectrum of color - else they would have limited utility as 'white' LEDs, yes?

..If one had a choice of color to be used in "murky" water....what color what that light be?

In general, colors farthest away in terms of spectral distance from the dominant color of the water as seen in daylight.

Say, for example, the water has a greenish cast when seen in sunlight from above. Green, at around 530 nm wavelength, is more or less in the middle of the visible spectrum. The fact that the *reflected color* of the water looks green means that the particles in the water tend to backscatter green light whilst letting other colors less like green to pass through.

Algae, other microscopic organisms and organic debris are of course a completely different problem altogether; I'm speaking here strictly in terms of particle reflectance as a function of wavelength. The actual case in real, Missouri River water will be complicated by other factors. That being said, the colors farthest from green would be red (700 nm) and violet (400 nm). There is also the matter of absorption. What color is the water when you look through it?

The easiest way to sidestep all this spectrographic handwaving is to simply try various combinations of light from red, green and blue LEDs and 'tune' the mix of colors to one which affords the best results.

http://www.summitracing.com/parts/RGD-70211?seid=srese2

This is what they have. It seems it only comes in white. I will convey what you have said to these biologists and let them hunt for some colors to try. The present LED set up works better than the Q-beam, but the river and its channels change color and hue with the seasons...at some time it does get a light greenish. I think there is ground for improvement with this light system , as the gear they are using is a surface fishing gear and they are sampling fish that are extremely fast as well as small.

Thank you and all that contributed.

They may want to test and install one light underwater to cut down on surface refraction and glare

One of these might be worth a try. 72 watts, 4300 lumens. Green illumination, possibly not so much for penetrating turbid water, but possibly because the green color attracts fish more than other colors? They are trying to catch fish, yes?

@netmaker, I think this outfit is in Houston. You're in Louisiana, I believe? Cajun country? (home of the best shrimp etouffe on the planet)

According to the site, this light MUST submerged when operating, for cooling purposes. Out of water it'll overheat in about two minutes.

Good idea to use Green light or even Amber. It is essential to be away from blue band of light scattering in sea water is good.

That is the gadget. However I have seen some models in various colors. Very popular in Florida with the upscale yachtie crowd.

All of them run so hot they require immersion for cooling.

Wavelengths shorter than Red, try from Amber, Yellow to Green but larger than Blue are the best. One can also try Sodium Yellow color.

Amber and Yellow power LED will be the best but CCD camera and human eye have greater response for Green.

If it's deep seawater far out to sea, blue and green work best.

In this case it is a freshwater river (the Missouri River) with variable levels of turbidity with variable composition. Not the most ideal circumstances for any visible wavelength.

Rebel Design specifically mentions muddy or turbid water such as rivers. They say a white LED has a yellow cast of color in muddy water and green still reaches further than blue. The installation photos bear this out. The fourth hit on the list was for a website showing all manner of installations and several colors. Marinas in rivers quite often has poor visibility water. Don't take my word for it. Go look at the websites yourself. In the first couple of pages I saw half a dozen manufacturers or suppliers. Very informative and colorful. There was also a You Tube instructional on how to install such lights.

Visited the site. Thanks.

If you Google "Underwater LED lights" you will get many pages of hits several of which have photographs clearly showing how each color reaches under water. Green looks to be the best bet and is also recommended by several suppliers.

For net trawling I suppose you could even consider installing the lights on the spreader bar holding the top of the net open. It would facilitate inspecting the catch before hauling it inboard.

Sounds like a fun project!

Actually no they don't, "white" led's, like flourescent lights, have three narrow color peaks that merge to appear white to our eyes,as well as a near UV emission as well. Blue and UV penetrate water quite well, in fact the Navy was looking into using satellite based UV lasers to communicate with shallow running subs so they didn't have to breach the surface, but ELF was still good enough and could reach deeper and didn't have problems with cloud cover so the project was scrapped I think. the incandescent lamp has a true "black body" broad range thermal emission band that peaks in the yellow range which is scattered much more in water. IR, red, green, and yellow LED's are color specific because of the specific semiconductor junction used, all other LED's are based on Silicon Carbide blue/near UV led's with different phosphor mixes in the plastic encapsulant. They work differently from conventional LED's.

THIS is what they are doing with my nets.

They want to try this at night and would like to see how these Asian Carp react, underwater, at night...when approached by the net.

Are these your guys or is this a video of someone else in a different river doing the same thing?

Those carp are leaping out ahead of the boat and far to the side. How are they going to put the lights that far out? Booms, with the lights trailing underwater?

These are MY nets and my customers. The frame work is my design but their modifications.

These fish are super spooky and sensitive to any disturbance. Look at the Starboard (Right) side. They bring in about 200 lbs of fish. there are not as many escapees as you might think.

At night, everything changes and the fish react differently. What they want to see is what is happening INSIDE the net once the fish enter. what you do not see is the fish being stunned under water by the pulse put out by the shocking unit. Any fish within 12' of that rig is stunned motionless for about 6 seconds...plenty of time to be scooped up. Just the fish jumping to the left or right stand a chance...some of these turn into the pulse array when they are under water.

Since this video, the new FlatWing Paupiers double this amount in catch....much more efficient. Still, the USFWS want to see what is happening INSIDE the net.

Sonar from a Didson helped but turbidity makes for a poor sonar picture.

Where is the link to the video being discussed? Thanks.

I reckon several of those green lights would be ideal in this scenario. They'd probably want to mount the lights horizontally under water near the boat and maybe with a strip of aluminum metal tape across the topmost side so that the fish are not lost in the glare (at 4300 lumens, these lights are damn bright). Aluminum tape (such as used to seal joints in ductwork) so that it will 1) facilitate cooling and 2) act to reflect the light outward/downward toward the fish and away from the observers. I'd try different placements to see what works best, using hefty nylon cable ties to anchor the lights in place (Home Depot, Lowe's, et al), at least if they use the frame for mounting. From the video it's a bit hard to see how things are arranged underwater.

What video?? have you got a link?

Post #26?

Thank you!

With my impaired vision I missed that. Letters are blurred and I had to use a magnifier to recognize it. Pictures are not so hard. Its easier to guess at what I'm seeing.

As you might imagine several factors can affect the ability of a beam to help you see something underwater.

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If the beam originates above water, reflectance at the water surface is the first big obstacle. Spectral reflectance is problematic in part because it reduces the amount of light that makes it beneath the surface, but also because intense glare at the surface can make it difficult to detect more subtle patterns beneath the surface.

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There are some variations in spectral reflectance, generally with blue green wavelengths being reflected more strongly than red wavelengths, as you would expect since water typically appears blue green and not red. The importance of the wavelength variations in spectral reflectance don't end up being something that can easily be put to good use though.

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Polarization of light can be put to good use for beams that originate above the surface and enter the water at angles other than close to perpendicular. Note the advantage for p polarized light for any angle off normal around 30 degrees and above.

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A much easier and very effective option for dealing with specular reflectance for light that originating above the surface is simply to contain all of the reflection. Growing up I use to gig mullet and flounder at night from the front of a jonboat with a very effective and cheap lighting set up that consisted of an upside-down styrofoam cooler, without the lid, floating on the water tied off the bow with a bright light suspended inside the cooler. because all the sides made contact with the water, none of the reflected light glared up and essentially only beneath the water was illuminated.

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Once the light is beneath the surface there are a couple more effects that come into play, transmittance at various wavelengths of just water itself, volume reflectance for varying turbidity, and volume reflectance with varying chlorophyll concentrations.

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Water absorption of longer wavelength visible light is pretty strong. Red wavelengths are almost completely gone, and orange wavelengths cut in half, traveling through 10 to 12 feet of water. With greater distance, yellows rapidly diminish and even greens are drastically cut. Traveling more than 50 ft total, blue and violet wavelengths make up the vast majority of what remains. This is why taking a strong light scuba diving can be very worthwhile, even diving mid-day in very clear water.

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Turbidity is different in that the problem isn't that the light is absorbed, but that it is reflected making things cloudy. Shorter wavelengths fair far better than others...

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Chlorophyll presents the same volume reflection problem, but the curves for various wavelengths are different. Note the high reflectance at lower concentrations in the short wavelength region.

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here is another look. but phytoplankton as a proxy for chlorophyll

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Okay, so to review, once the light is underwater, longer wavelengths putter out really quickly, shorter wavelengths do better with turbidity, and there is a sweet spot that works with varying levels of chlorophyll in the 475 nm to 515 nm... and avoiding wavelengths above and below that.

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Here are some various light wavelength spectrum to consider.

Nothing looks particularly good from that selection...

Something like the spectrum for this LED would probably be ideal....

So with murky, turbid like water you would go with a green or purple color?

The water quality will change to greenish later on ( possibly 1 meter or so on a Seechi Disk ).

A light with a fairly tight spectrum centered anywhere from 480 nm to 510 nm, so cyan, is going to work well over a wide range of conditions.

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If you could be certain that was either absolutely no chlorophyll or alternately a significant amount of chlorophyll, then shorter wavelengths would be better, so blues and violets, basically anything at or below cyan.

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Non-white LEDs give some great options to use very narrow bands, where as most other light sources are going to have a lot of light in wavelengths that may make it harder to see.

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If the water has lots of chlorophyll, but otherwise turbidity is low, there is a small window for a narrow band LED to suppliment lighting around the 590 nm range. It would be best to put LEDs like that as close to the fish as possible since the range in water is less, so perhaps at the most outboard part of the net frames.

Just a word of caution: if they're thinking of using the lights they have now, underwater, there is the potential of water entering the housing via that pressure equalization vent (bottom item):

Rigid Industries M-series D2 lights feature:

* 50,000 plus hours LED life span
* Instant on/off--no warm up
* RoHS compliant
* Over/under voltage protection
* Cast aluminum housing
* Chromate corrosion-resistant coating
* UV-resistant powdercoating
* Durable and optically clear polycarbonate lens
* Integrated thermal management
* GORE pressure equalizing vent ^{_{(image representative of this type of vent)}}

Thank you for all the information you posted concerning this inquiry.

The LED transmit a more directional light beam (a kind of lobe). It's like a spot light.

So we don't get too far away from where I wanted to be:

The crew wants to view THIS spot... about 2 meters back from the frame , about 2 meters wide and anywhere from .5 to 1 meter deep ( when water is clear).

The lights need to be mounted as shown ...on the support rail about a meter up from the gunwale. Daytime is no issue. Its at night , when the water clears up in the Summer that they want to see under the water and into the net.

For those that missed the video showing the use of this gear, View here.

SIDE NOTE:

IF you all remember a Question I asked you all a year ago, Dampening Vibration of Cables. . . . this is the gear that discussion was all about. Problem was solved by dropping steel cables all together and going with 8 strand Dyneema braided line. .....and I thank everyone who participated in THAT discussion also.

I'd use one or more of those underwater LED lights Europium mentioned earlier on a two part sling going to a short PVC pipe with rings on either end as a spreader bar so it trails behind the boom above the net. I think I'd use blue LED's myself...

Hi Netmaker

Change the lights to laser, pump up the power, add a pattern generator and .... you won't even need the netting...

The Icelanders have been experimenting with laser trawl gear for some time now:

A conventional trawl is shown on the right and the laser trawl on the left. A normal netting-type codend is still required to hold the catch.

Thank you Maurice. What we have is a simple Paupier Surface trawl gear for taking samples of Asian carp in the Midwest river systems. These guys take a few hundred specimens and that is all. No one wants a commercial haul. As for the lighting, they want to see what happens inside the net as I have two devices built inside that hold some species and release other. No need to harm anything that is NOT on their "hit list"..

As for the Icelanders...they are going to fish themselves out of living one day.. . . if they haven't already. . . . ha ha !

Can you illuminate (pardon the pun, but I couldn't help myself ) me on what "diurnal fish work" is?

My understanding of a diurnal creature is one that sleeps at night and is awake during the day (opposite of nocturnal).

Netmaker can probably fil in blanks, but my understanding is that the fish (asian carp) react to trawls differently at night vs during the day. The biologists are studying this as a possible means to capture them preferentially in trawl nets while leaving more of the native species alone.

...Could not have put it better!

Very little work has been done on Asian carp at night. this summer we have an array of prototype, target-specific gears that will concentrate on these fish. I'll post what the government allow me to post during the trials....

Meanwhile, the biologists have discovered that some of the gear we built for YOY Asian carp, also captures some rare and even endangered species in the Young of the Year phase ( 5-50mm in length). A win-win situation for everybody.

Thank Rorschach for the explanation...it was right on target ( windage and elevation taken into account) ha ha !

I am assuming that the biologists aren't releasing any carp they catch during the studies...

By federal law they can not.

Thanks

..."Can you illuminate (pardon the pun, but I couldn't help myself ) me on what "diurnal fish work" is?"

Many fish species stay in deeper water during the day and rise up in the water column at night.We build specific gear that gently picks these critters up for examination, release, or live catch for museums. Some gear takes them in their deep environs: Aluette Midwater trawls or SKT Benthic trawls,. . . . . some gear take them on the surface; Mamou,Paupier and Canard trawl nets.

The list includes some Great Lakes fishes, bioluminescent fish in the Pacific, some squid, etc. Its just a phrase we use or maybe mis-use .... I deal with folks smarter than I am , but I do get to name the gear ! Still, Wikipedia I ain't! ha ha!

Thanks