Flat Mask Comparison above and below water. Image by: Jon Kranhouse

Every wonder why we can’t see properly under water? Well, I looked it up. Our eyes are adapted for viewing in a gaseous (air) environment. Light rays bend less through gasses than they would underwater. In water, light rays are refracted much differently. So how does that affect me? Well, if you like to dive or snorkel it affects three key things: Color, Distance and size. We wear goggles to see underwater. The reason why this works is because of the layer of air between the glass making the light refracts “normally” for us. Keep in mind though that with those goggles on, things will look about 33% bigger in freshwater, 34% bigger in saltwater and 25% closer overall. Our color perception underwater changes the deeper you are and the more particles and how muddy/murky it is in the first place. The following is a guide by Luria et al.

A. For murky, turbid water of low visibility (rivers, harbors, etc.)
1. With natural illumination:
a. Fluorescent yellow, orange, and red.
b. Regular yellow, orange, and white.

2. With incandescent illumination:
a. Fluorescent and regular yellow, orange, red and white.

3. With a mercury light source:
a. Fluorescent yellow-green and yellow-orange.
b. Regular yellow and white.

B. For moderately turbid water (sounds, bays, coastal water).
1. With natural illumination or incandescent light source:
a. Any fluorescent in the yellows, oranges, and reds.
b. Regular yellow, orange, and white.

2. With a mercury light source:
a. Fluorescent yellow-green and yellow-orange.
b. Regular yellow and white.

C. For clear water (southern water, deep water off shore, etc.).
1. With any type of illumination fluorescent paints are superior.
a. With long viewing distances, fluorescent green and yellow-green.
b. With short viewing distances, fluorescent orange is excellent.

2. With natural illumination:
a. Fluorescent paints.
b. Regular yellow, orange, and white.

3. With incandescent light source:
a. Fluorescent paints.
b. Regular yellow, orange, and white.

4. With a mercury light source:
a. Fluorescent paints.
b. Regular yellow, white.

The most difficult colors at the limits of visibility with a water
background are dark colors such as gray or black.