By farVisual perception(*) the largest part of our perception of the environment is due to our eyes. However, visual perception is a complicated process. On the one hand, a stimulus entering the eye from the outside can be physically characterised by the spectrum of incident electromagnetic radiation. The spectral range perceivable by the eye is called light. Some of it is reflected and another wavelength-dependent part is absorbed in the interior of the eye. The remaining radiation hits the retina with the actual light detectors, the photoreceptor cells.