There is no natural light below 1000m and most organisms have small or absent eyes to account for this. However, some organisms have developed bioluminescence, either synthesized by their own body or through a symbiotic relationship with bacteria. It has various uses from locating or luring prey to confusing predators and even enabling communication between organisms of the same species, for example to aid finding a mate. The colour of light most often produced by organisms is a blue-green, which is the colour that penetrates farthest through water and so is visible to other organisms at the greatest possible range (Herring 2001). The following gives some examples of organisms which have adapted to using bioluminescence, bringing light to a world of utter darkness (Figure 2).