Refraction
Refraction is a property of light that refers to the change in the
speed of light due to change of density in a new medium. This causes a
change in the light's path. An example of this is given by looking at a
pencil partially submerged in a clear glass of water. The pencil
appears as if it is bent. This is because the path of the light you are
seeing changes when the light passes through the water. While
underwater,
this property can make things appear closer to you than
they actually are.
Reversal
While refraction can make things appear closer
to you than they actually are, turbidity, or the concentration of
suspended particles in the water, can make objects appear further away
than they actually are. This is referred to as visual reversal.
Reflection
When light strikes something, it may be
reflected or absorbed. The amount of light reflected or absorbed can
depend upon the substance that the light is striking. For some
substances such as water, the amount of light reflected is related to
the angle at which the light hits the surface of the water. When the
angle between the light source, in this case the sun, and the plane of
the surface of the water is 90 degrees, almost no light is reflected.
As this angle decreases, a greater amount of light is reflected. This
is why a diver in relatively clear water will experience brighter dive
conditions at noon than at twilight.
Color Absorption
The colors that we see all have different
wavelengths. These wavelengths relate to the amount of energy in the
light. As light passes through water, wavelengths with less energy are
more easily absorbed. Because of this, the deeper a diver descends, the
less colors that he or she can see. When underwater photographers take
photos, they use powerful lights to illuminate their subject. This
introduces a new, closer light source thereby 'reintroducing' color.