|This is a real image of a marine amphipod without any fancy photoshop tricks. Understanding these diamond-like patterns will require knowledge about polarized light and the role of polarized vision in marine invertebrates.|
When light reaches our eyes we detect wavelength (color) and wave intensity (brightness) information. That is exactly what the brain needs to build a visual picture of the surrounding world. Yet a lot of other information is left out. UV and infrared parts of the spectrum are the most obvious examples. Well, technically the human retina is sensitive to UV, but the eye lens filters it out. That is why individuals missing eye lens, for example due to cataract surgery, can see UV light. Some parts of infrared waves can be sensed by the skin as heat, which is how we can estimate whether a frying pan is hot or not. These features, however, don’t make up for the limitation of our vision.
Aside from having a very narrow spectral sensitivity we can’t detect light wave oscillation direction, which is another parameter of a wave in addition to wavelength and intensity. In the majority of cases each individual wave vibrates in a random orientation in a natural beam of light. This did not prevent many types of invertebrates, birds, and fish from finding another visual world by means of enabling themselves to sense additional dimension of light—polarization and its angle.