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Light Absorption at Depth

If you think back to your dive training you will recall that colours diminish the deeper you go. If you have been on one of Herts Dive Club’s Red Sea trips on a deep reef, you may recall noticing that the bright red sea fans and diverse colours you were used to seeing in photos didn’t exactly match what you saw in real life. As we know, this is because, as you descend deeper, water filters out colour.

In the video above diver Kendall Roberg, built a rig with marker caps attached to his GoPro to show how colours change as you go deeper. He dives to 155 feet (47 meters), showing the spectrum transitioning from a vibrant rainbow to a cooler-toned array.

Colour loss occurs gradually because water absorbs different wavelengths of light at different degrees. The longer the wavelength, the lower the energy. These wavelengths get absorbed first. The order in which colours are absorbed is the order in which they appear in a rainbow: red goes first, with violet going second-to-last and ultraviolet being last to disappear. You may have noticed that the neon-pink cap (which has ultraviolet light) is vibrant throughout the whole video, even after the red cap has changed completely.

The changing colours are especially important to take into account as an underwater photographer: To shoot photos underwater that aren’t washed out, use filters, strobes, photo and video lights, and special settings to compensate for the lack of light.

However, all divers can miss out on the beauty and diversity of the underwater world without tools to compensate for the absorption of light. For example, using a dive light or getting a mask with tinted lenses can help you see more colours.

graph showing how light is absorbed underwater

If you would like to learn more sign up for the PADI Advanced Open Water Course. The next course is running on 28th – 29th April at Stoney Cove. Details of the event can be found here or click the button to book now. (Limited spaces available)

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