Science and research
Normal", that is visible light, is a type of electromagnetic wave. The distinguishing feature of each wave is its length or frequency.
The lens is an important element of the eye of mammals, birds, reptiles, amphibians, and fish. It allows one to see objects located at different distances clearly. It is possible because images are formed on the retina - another important part of the eye. Clear images are achieved by changes in the shape of the lens.