Why is there such a harsh light decrease the deeper you go under water? Why do photos that are taken under water often show a blue-green color shading? Everyone who has engaged in under water photography, has probably already asked himself such questions. In order to understand this phenomenon, it is necessary to take a look at the properties of light. In the first part of our series “how does water affect the properties of light?”, we will take a look at the light spectrum.
The spectrum of the visible light
The visible light is the range of electromagnetic radiation, which can be detected by the human eye (aprox. 400-700 nm). Close to this range, yet invisible to the human eye, wavelengths of the infrared radiation (aprox. 780 nm – 50um) and UV radiation (aprox. 1nm-380nm) can be found. Electromagnetic radiation can be described by two physical quantities, namely wavelength and frequency. The wavelength is the distance a wave travels per oscillation, for instance from one wave peak to the next wave peak, whereas the frequency describes the amount of oscillations per unit of time.
Color absorption under water
Different conditions apply under water. The water will gradually filter out the colors with increase in depth. Depending on the respective wavelength, some colors will be absorbed earlier than others. The color red for instance, already disappears within a couple of meters of depth, whereas the color blue won’t be gone until one is about 60 meters deep. The shorter the wave length of a color, the farther it can be seen.
If one dives below 60 meters, all colors are absorbed and the diver is surrounded by darkness. This phenomenon is called extinction. This law applies to the color visibility in horizontal direction as well, and therefore the visual range is limited to 60 meters simply due to light absorption. In addition to that, other factors like dissolved matter or floating particles may further decrease the visual range.
Now where does the dive light come in to play? Is it possible to counterbalance the color deficits under water? Which color temperature is suited best to illuminate the under water environment ideally? Those questions among others will be subject of our next article: Color temperature and dive lights.