Loss of Light and Loss of Colour

Topics concerning the difficulty of light and colour loss underwater have become so hackneyed in recent years that it is a challenge to grab the attention of an audience. Let's face it, most of you have seen and heard it many times before, both in pictures and words! Light and colour are absorbed at depth, blar, blar, etc, etc. However, my experience in reality is that although these basics are common place, sometimes they don't really 'sink in'. That is, until one is comparing one's underwater efforts with another and on the same dive, same place, same time, same camera, a disparity is suddenly revealed. Their underwater photos are better than mine!

'How can that be the case, we were using the same camera'?'

'We were shooting the same subject side by side and what's more, I found it first.'

This is where I tend to become involved.

'Martin, can you look over our shots, I don't seem to be getting the colour and clarity like everyone else.'

From my experiencing of teaching you can be assured without a shadow of doubt that the reality of light and colour loss will one day catch up with you if you do not understand and work hard to remember the principles whilst you're shooting. I find that beginners often forget that horizontal distance also reduces light and colour. If you are 7 m deep and 3 m from your subject, the total light path is actually equal to 10 m. For another example, cast your mind back to an occasion of good visibility in 10 m of water. Can you remember that your eye saw a much more colourful spectacle than your camera was able to record? This was because your brain compensated for the blue colour cast and effectively 'saturated' the warmer colours. Your camera cannot perform these tasks by itself, it needs some help from you, and by understanding the fundamentals of how light behaves underwater you will be able to take greater control of your underwater photography.

The behaviour of light underwater is unlike the behaviour of light on land. For starters, the density of water is 800 times that of air. Such is this density that we can compare a picture taken in 1 m of water with a picture on land taken at 800 m away.

• As soon as light enters the water it also interacts with suspended particles, resulting in a loss of both colour and contrast.

• Particulates and water molecules react with the light entering the sea, and it immediately begins to be absorbed.

FIG. 1.41 The filtration effects of colour according to depth.

FIG. 1.41 The filtration effects of colour according to depth.

Loss Colour Underwater

• Red goes first, then orange and yellow, until only green and blue are left. So rapid is the loss of red that within half a metre of the surface those red swimming shorts are muted and dull.

• Even in the best imaginable visibility, particulates are suspended in the water column. In a typical tropical diving destination with good visibility, these particulates tend to reflect and scatter light as they move through the water. Whilst you can reduce their effects, you can never eliminate them entirely.

It is also important for the underwater photographer to recognise that:

• The conditions on the surface have an effect on how light passes through the water.

• Calm seas allow more light to pass through whilst a choppy sea reflects light.

• The position of the sun in the sky and the time of day also have an effect on the amount of light entering the water.

• When the sun is high in the sky over a flat calm sea, most of the sun's rays pass through the surface. As the sun arcs closer to the horizon the light loss due to the angle of refraction against the water surface increases dramatically.

The light which does penetrate at these times is usually soft and diffused and I

find it the most inspiring and magical time of day to take natural light photos underwater, although if you want to take pictures when the sun is high in the sky the best lighting conditions are between 1000 and 1400 hrs.

Rough waters reflect and disperse most of the sun's light rays

Calm water allows greatest light penetration

Rough waters reflect and disperse most of the sun's light rays

Calm water allows greatest light penetration

Low-angle sunlight is reflected

High-angle sunlight penetrates water surface

Clouds diffuse and reflect light rays

Low-angle sunlight is reflected

High-angle sunlight penetrates water surface

Clouds diffuse and reflect light rays

Radial light FIG. 1.42 The behaviour of natural light underwater.
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Responses

  • fatima
    How light behaves underwater?
    7 years ago

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