This page is just a few quick notes about light and heat and the important things you should know about these topics before you strap on a tank.
Divers have to wear thermal protection in temperatures that would be comfy in air because water conducts heat better than air. So it will conduct heat away from you much faster!
Water also has a high heat capacity.
It would take 3200 times as much heat to raise a given volume of water to a specific temperature as it would to raise the same volume of air to the same temperature.
Your eyes see things by collecting light reflected from the object you are looking at. Light behaves differently in the air and water, so the same things can be seen differently.
As far as light and the SCUBA diver, a few things are important. First, check out the photo to the left.
The photo shows the depth that different wavelengths of visible light get absorbed at in the water column. The first color to disappear is red, which is why underwater photographers often use red filters or bright flashes to restore red colors in the pictures.
The last color to be absorbed is blue at 76m, which is why everything looks so blue at depth. After the blue light disappears you will need a flashlight. Actually, this is much deeper than the recreational dive limit of 40m, so you might just want to get a mask with a cool red filter coating and bring a light ort two for night dives.
Another thing about light is that it travels at different speeds in different substances. When it passes through a different medium the angle of the light changes. So the refraction of light coming through the water and into the air inside your mask makes objects underwater appear larger by a ratio of 4:3.
So don't forget to tell lots of fish stories when you get back from your trip!