Physically, the phenomenon of light can be described with two main conceptual models:
On the one hand, light obeys the laws of wave theory in wide macroscopic areas. For this reason, monochromatic light can be described fairly well as continuous electromagnetic radiation of a certain frequency and intensity. Specific frequencies or wavelengths can be assigned to the various types of light (IR, visible light, UV, but also the individual colours). If we arrange them in the order of these wavelengths, this results in the well-known spectrum of visible light.
Here, the frequency of the individual colours corresponds to the relative energy content of the light. In relative terms, therefore, red light has less energy than blue light. Infrared light also has considerably less energy than ultraviolet light.
A different approach is based on the quantum physical properties of light. If we leave the macroscopic field, light (and other forms of electromagnetic radiation) is shown to have a discontinuous nature.
The radiant energy is not transmitted continuously – as in wave theory. On the contrary, the energy seems to be characterised by a certain granularity. Light, therefore, cannot be transmitted in slices of arbitrary size, but is transported through the transmission of tiny units. Planck was the first to discover this phenomenon, and he coined the term Planck’s constant. By analogy to wave theory, each light quantum has a specific energy, which corresponds to its colour or wavelength. The individual light quantum is indivisible, and so monochromatic light can be shown as a multiple of such a light quantum.
Both theories have their justification and differ mainly in the standards in which they are valid. This is called wave-particle duality. Since this guide only covers the microscopic area, the wave theory will mainly be used in the following.
In an even broader context, light can also be represented in a simplified ray model. Here, rays of light are formed along a connecting line between the light source and a target point to be viewed. Many relevant optical phenomena, like reflection, refraction and scatter, can be described relatively exactly with this simple model.
As already mentioned above, it is possible to represent monochromatic light by means of a specific wavelength. According to the superposition principle, light waves can be freely mixed.
Mixing individual monochromatic components creates mixed light. If one looks at the spectral composition of such light, the individual monochromatic components can be identified and separated even after mixing. The wave properties of the types of light originally used thus remain intact. The mixing of individual monochromatic components to form polychromatic light can be extended at will. To put it very simply: if a spectrum contains light of all visible wavelengths, and if their intensities are suitably distributed, this light appears to us to have a white colour. Here, ideal white light is represented by the spectrum of the sun.
The quality of an artificial light source must always be comparable with the characteristics of sunlight since, as a result of a development lasting several million years, our eyes have adapted to this light quality.
