Effects of Water Depth on Color Visibility
Written by Capt. Gregory Houtteman   
Sunday, 31 December 2006 19:12

Determining what colors are visible at various depths of water is quite literally a science, an analysis of the physics of how light interacts with water particles and other light absorbing particles that may be present in water.  Now everyone break out their slide rule, put your propeller beanie on, and calculate what colors are visible at my 100 foot deep downrigger weight using complex multivariate formulas.  Hurry up, c’mon.

What do you do when you’ve forgotten your slide rule or like me your calculator batteries have died again?  You use common sense rules that can help you determine what colors are likely to be visible at certain depths. 

Understand that light contains all of the visible colors and each color has a unique wavelength.  No need to break out that slide rule.  When full spectrum light, often referred to as white light, hits an object two things happen; the object reflects and absorbs certain wavelengths of that white light. 

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Absolute loss of color - this is not what is visible to the eye - this is the total loss of particular wave lengths - Courtesy of NOAA
The reflected light is the color that we see, think of it as what “bounces” back off the object to our eyes.  White objects are those that reflect most or all of the light back to our eyes and black objects are those that absorb most or all of the light.

The spoons, flies, and attractors that we use everyday are reflecting and absorbing different wavelengths of light determining what color we see when they are in the back of the boat.  Put those in the water and things begin to change almost immediately.  Water particles interact with light in a much different way than air, light wavelengths are being absorbed by the water particles, the deeper the water the more wavelengths are absorbed.   If those wavelengths are already absorbed at certain depths then there is nothing to reflect off our beautiful lures and those colors are no longer visible.

Given perfect conditions, red and oranges are the first colors to disappear, to be absorbed by the water, followed later by yellows, greens, purples, and blues in that order.  Take into account that this is a general rule of thumb because light absorption can be affected by what is suspended in the water.Things like plankton or sediment can reflect or absorb colors before they would normally be absorbed in clear water.

 

 

There are many other factors that affect how light penetrates water including the state of the waves.  Flat calm water will reflect a large portion of light diminishing the intensity of the light that is entering the water.That’s why we really need those sunglasses on the calm sunny days.  On choppy days, we get better light penetration but somewhat scattered…and on wavy days we get a diffused light entering the water affecting light penetration. 

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The angle of the light plays a big role in light penetration.  As the sun comes up and sets during the daylight cycle the light from the sun will be hitting the surface of the water at different angles.  The best light penetration occurs during the most direct sunlight period, high noon, when the sun is closest to a 90% angle to the water surface.  At angles of 40% or less to the water surface light penetration falls off dramatically, these periods coincide with sunrise and sunset.

Clarity of water is also a big factor in light penetration and color absorption, the clearer the water the deeper all wavelengths of light will reach.  Factors such as phytoplankton and zooplankton suspended in the water, along with sediment such as sand or mud all affect light penetration and affect which colors get absorbed; this does not mean that other wavelengths are affected negatively.

The most common factor that changes the penetration depth of light in water is the amount of light available; a simple principle, if it’s cloudy and dark there is less light available to enter the water.  While you can still get sunburn on a cloudy day, UVA and UVB rays are not visible; you need “white light” to determine color.   While you can still see color when it’s cloudy on the back of the boat less light means less light penetration through the water, which will affect the depths at which colors disappear.

Wow!  What does this all mean to me as an angler?  Since we have all agreed that we aren’t going to break out the slide rule, use the information to make some educated assumptions.  Start at the light penetration baseline of perfect light with clear water and work back from there.  Assume that on a perfect day red is only going to be visible to depths of 15 feet, but because of clouds I know that it may only be 10 feet today, or because the water isn’t completely clear, or because it is early morning or late in the day.  It is not absolutely necessary to know the exact depths.Would it be nice? Yes.  But what is important is to have a general idea of what is going on down deep where you can’t see.

Now that we got all the technical stuff out of the way, how do we apply this to our fishing?  If you’re running red or orange lures, flies, or flashers and running them below 20 or 30 feet then the color is not showing, these colors are showing as brown or black.  This means that if you’re having success with these lures it is not due to the orange or red color, it may be related to the action, the flash, perhaps some glow paint or tape, or the fact that it is actually showing black or brown in color.  This holds true as we move down in depth with the other colors as their wavelengths disappear.

Have you ever wondered why people say to use bright lures on bright days, and dark lures on dark days?  Does it make sense now that you know something about light penetration? NO?  O.K., I’ll try to explain.

First of all, bright colored lures are typically considered those of the orange, red, green, and yellow variety; which are most effective on those beautiful bright days.  So if it’s dark and nasty out, running bright colors has little effect because unless they are being run totally on the surface those colors are not visible.  Why run dark lures on dark day then?  Because the colors aren’t going to show, it becomes a matter of contrast, lure action, and lure size, and dark lures contrast more effectively on dark days because they are darker to start with.  For instance an orange lure down deep might work, but it is really showing a soft brown where as a black lure is showing solid black and a hard edge.

This is not the definitive guide to what colors to run when.  It is simply a primer of what is happening on any given day.  Next time you are out on the water think about the effects of color loss at water depth and start to apply that understanding to what is happening in your fishing.  Begin to take into account the use of glow tape, glow and super glow paint as they affect the visibility of lures, regardless of color. 

While the effects of water depth on color loss are a science, effective lure selection is not.  Hopefully these guidelines will become another tool that helps you become more efficient when out on the water.

 
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