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 aka Underwater Vision

Have you ever watched a television show or movie that was filmed underwater? As the scuba diver and camera descend from the surface, what happens to the colors of the plants an animals? Before too long, everything appears blue! Discover why everything is blue, and how some creatures have evolved "sniper goggles" that take advantage of this deep blue world.



  • Large fabric swatches (1 meter square or larger), preferably of an underwater ocean scene, such as blue backgrounds with red and/or multicolored fish. AVOID THOSE FABRICS WITH ANY WHITE IN THEM.
  • Blue "party" bulb with socket
  • Red "party" bulb with socket
  • Electrical power strip (and extension cord if needed)
  • Blue cellophane strip (e.g. transparent blue report covers)



This works best if done in a room that can be made TOTALLY dark.

1. Spread out the fabric on a table or hang on a wall. Plug the power strip into an electrical outlet and place it near the fabric - use an extension cord if necessary. Place the blue bulb's socket into the strip. Make sure that all participants have a blue cellophane strip.

2. Turn off the lights. Turn on the blue light and shine it at the fabric. What do you see? Do any colors stand out? Try using the blue filters to look through - does that change what you see? How does the image you see with the blue light compare to what you see when "white" lights are on?

3. Keep the blue light on, but now insert the red light into the strip. Shine both of these lights on the image. Examine the image without the cellophane strip; do the images on the fabric look different than with the blue light alone? Look through the blue filter (double it so that it's two layers thick). When you look through the double blue filter with the red light on, how does what you see change?



When the "regular" lights are turned off and blue light is shined on the fabric, most colors will look dark and the only discernable color will be blue. Since there is only blue light as a source, blue-colored images will reflect the blue light. Other colors will absorb the blue light and appear as dark shadows in the blue field.

When you turn on the red light, images that are red, and to a lesser extent orange and yellow, will reflect the red light. When you look through the blue filter, the red images again become dark shadows because the blue filter only transmits blue light, and absorb the red light reflected from the red images.



As one descends from the ocean's surface to its bottom, the amount and quality of available light changes. Long wavelengths of light, such as red, are absorbed by the water within the first few feet. Sea water is more transparent to shorter wavelengths of light, such as blue which penetrates the most deeply.

Blue light is the only visible (to humans) wavelength the penetrates water to about 33 meters (100 feet) depth. If we view an object at that depth, it would appear blue - think of deep underwater photographs and films. Beyond about 1500 meters in depth no light penetrates (this is called the aphotic zone).

At about 33 meters or deeper in sea water, only blue light penetrates. From here to the aphotic zone, most animals only see blue -- they have lost their ability to see other colors, because they don't normally encounter them. When you look at the images with the blue light, this may approximate the colors these creatures see. (Looking through the blue filter may help filter out any stray light).



Since most deep sea creatures can only see blue light, being colored red provides an excellent camouflage from predators -- they will blend in with the dark background. However, in a "nature did it first" event, at least one species of fish has evolved to take advantage of this situation.

One species of angler fish has evolved a light-emitting photophore on a "lure" extending from its head. The photophore emits red light, and the anglerfish has retained its ability to see red! It uses the photophore as a "sniper goggle" illuminating its surroundings. It can actually see red-colored prey, but since few other species can see red, the prey is unaware of the approaching danger! Adding the red light to the activity models the red light produced by this fish and what they see. Interestingly, this species of anglerfish is a reddish color, perhaps to aid them finding each other for mating purposes as well as remaining camouflaged to potential prey.

Copyright KK 2000

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