For light in the automotive sector, the so-called refraction is important. It occurs at the mirror, in the headlight, on windows and in fiber optics. Although light has particle and wave character here is now only the latter important. It is the geometrical optics with their straight course of light waves, which are mostly partially reflected at a flat surface.

The fact that to the vertical on the surface the angle of incidence equals the angle of reflection should be well known. Depending on the angle to the mirror surface, a real image is reproduced and is also created virtual picture. A situation, e.g. is exploited in dimming interior mirrors.

The angle of reflection is not equal to the angle of refraction. Depending on the material, the speed of light decreases, which makes the angle to the vertical smaller. This diminishes e.g. in water by about 25 percent and in glass by about 33 percent. If you look at the wave as a sinusoidal curve and its frequency is greater, then there are more waves per unit of time.

In the transition from a medium with a lower to one with a higher refractive index, the angle to the vertical changes very roughly by about the abovementioned percentages. Of course you can calcutale the change of the angle exactly. From a certain, rather larger angle of incidence total reflection occurs, the sooner the larger the refractive index of the material and the smaller the material behind that is. Almost all light is reflected then.

The emphasis is on 'almost', because a complete reflection does not take place. That it comes with every reflection to a certain attenuation (loss of light). Interestingly, this attenuation at total reflection and transparent glass is smaller than at a mirror with a lower angle of incidence. In fiber optics it is therefore important to keep this angle as large as possible, because then automatically occur less reflections per path length and thus a lower attenuation.

Now it becomes clear why plastic optical fibers should not be laid in tight bends, even though no light is emitted in these bends. Incidentally, the transition from material to relatively smaller refractive index to such with a larger avoided by surrounding the innermost optical fiber with an extremely thin layer (about 0.02 mm) of less refractive material.

Properly designed the light, e.g. in optical fibers, should reach up to 20 km. If you put in between suitable prisms in quick succession, even the transmission through another light pipe is possible. This design is called a light switch, but is not common for the automotive sector, because here anyway in each participant light is converted to electricity and light again.

It is astonishing how far optical fibers have become established in practice. With a bunch of them one can write fonts e.g. on traffic signs and signals, such as for the train. 01/18