What is the electromagnetic nature of light

Physical nature of light

Light in the narrower sense describes electromagnetic radiation that can be perceived with the human eye. In a broader physical sense, light denotes a larger area of ​​electromagnetic radiation, which is located between microwave radiation and X-ray radiation. In addition to visible light, this definition also includes infrared light and ultraviolet radiation.

Physically, the phenomenon of light can be described with two main thought models:
On the one hand, light obeys the laws of wave theory in large macroscopic areas. Monochromatic light can therefore be described quite well as continuous electromagnetic radiation of a certain frequency and intensity. The different types of light (IR, visible light, UV, but also the individual colors) can be assigned specific frequencies or wavelengths. Arranged according to these wavelengths, the known spectrum of visible light results.

The frequency of the individual colors corresponds to the relative energy content of the light. Red light is relatively less energetic than blue light. Infrared light is also significantly lower in energy than ultraviolet light.

Another way of looking at things is based on the quantum physical properties of light. If you leave the macroscopic area, light (and other electromagnetic radiation) has a discontinuous nature.

The radiation energy is not transferred continuously - as in the wave theory. Rather, the energy seems to be characterized by a certain graininess. Light cannot be transmitted in arbitrarily small bits, but is transported by transmitting the smallest units. Planck was the first to discover this phenomenon, he coined the concept of the quantum of action. In analogy to wave theory, each light quantum has a specific energy that corresponds to its color or wavelength. The individual light quantum is indivisible, so monochromatic light can be represented as a multiple of such a quantum.

Both theories are justified and differ mainly in the standards in which they are valid. This is known as wave-particle dualism. Since this guide only deals with the macroscopic area, the wave theory will mainly be used in the following.

In an even larger perspective, light can also be represented in a simplified ray model. Here, light rays are formed along a connecting line between the light source and a target point to be viewed. With this simple model, many relevant optical phenomena such as reflection, refraction and scattering can be described with sufficient accuracy.

As already mentioned at the beginning, it is possible to represent monochromatic light by means of a specific wavelength. Light waves can be freely mixed according to the superposition principle.

This mixing of individual monochromatic components creates mixed lights. 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 are therefore retained. The mixing of individual monochromatic components to form a polychromatic light can be expanded as required. In a very simplified way it can be said: If a spectrum contains light of all visible wavelengths and if their intensities are appropriately distributed, this light appears to us with a white color. The ideal white light is represented here by the spectrum of the sun.

The quality of an artificial light source must always be comparable to the characteristics of sunlight, as our eyes are adapted to this quality of light as a result of a development that has lasted several million years.

Sunlight is by far the essential source of energy for all life on earth. In other words, to put it simply, the producers (plants, algae, etc.) use photosynthetic processes to convert energy and inorganic raw materials into biomass. Photosynthesis based on chlorophyll is the most common. In this synthesis process, sugar is produced from carbon dioxide and water. This sugar (glucose), as an energy supplier for cell respiration, drives all further processes. The consumers (all animals, mushrooms and humans) consume the producers and thus participate indirectly in the photosynthetic energy production.

In addition to the supply of energy, sunlight, as one of the dominant natural phenomena, also has other, profound relationships with biological systems. The day-night rhythm of 24 hours represents the essential time cycle of nature. Many processes of living beings, including that of humans, are therefore influenced during the day by the changing nature of sunlight. The seasons of the earth regions remote from the equator are also directly linked to the phenomenon of light via the varying solar irradiation.

Radiation intensity of the sun