Light fraction

Light fraction describes the change in the direction of spread of light rays when it passes from one medium to another. This effect occurs because the speed of the light changes in different media, depending on its optical density. When entering a medium with a low density (e.g. air) in one with higher density (e.g. glass or water), the light is broken towards the normal. Conversely, it is broken away by the normal when it merges into a medium with a lower density.

The light fraction is responsible for numerous optical phenomena, such as pulling out of light rays in a prism, which makes the colors of light visible, or the formation of rainbows by breaking and reflecting the light in water drops. It is also an essential mechanism in optical devices such as lenses that bundle or dispel light, and has applications in glasses, microscopes and cameras.