What is light?
What is the nature of light, and what are the ways in which objects emit light?
Light is a form of energy that can travel from one object to another without any material intermediary. This energy transfer method is usually called radiation, which means that energy travels in all directions along a straight line (in the same medium) from the energy source. As early as the mid-17th century, Newton and Maxwell discussed the nature of light in detail with the "particle theory" and "wave theory" respectively, and it became the theoretical basis for the current public theory that light has "wave-particle duality". About 100 years ago, it was further confirmed that light is an electromagnetic wave, more strictly speaking, in the extremely broad and broad family of electromagnetic spectrum. The light waves of visible light occupy only a small amount of space.
It includes seven colors of violet, indigo, blue, green, orange, and red that can be distinguished by the human eye. Its long-wave direction is the infrared, microwave and radio wave regions with wavelengths ranging from micrometers to tens of kilometers. ; Its short-wave end is ultraviolet, x-ray, r-ray, and the wavelength of r-ray is so small that it can be compared with the diameter of an atom.
The light-emitting methods of objects can usually be divided into two categories, namely hot light and cold light. The so-called thermal light, also known as thermal radiation, refers to the heat emitted by substances at high temperatures. In the process of thermal radiation, the internal energy does not change, and the radiation can be carried out through heating. It radiates infrared light at low temperature and turns into white light at high temperature. It is well known that when a tungsten wire is heated to a very high temperature in a vacuum inert atmosphere, it emits an eye-catching white light. In fact, sunlight is the most common white light. The prism can decompose sunlight into the above seven colors. Experiments have proved that all the colors in nature can be synthesized as long as the three colors of blue, green and red are used. , including white light, we usually refer to the three colors blue, green and red as the three primary colors.
Cold light is the light emitted from a certain energy source at a lower temperature. When luminescent, an electron of an atom is excited from the ground state to a higher energy state by an external force. Because this state is unstable, the electron typically releases energy in the form of light, returning to the ground state. Since this luminescence process is not accompanied by the heating of the object, this form of light is called luminescence. According to the type of substance and the way of excitation, luminescence can be divided into various categories such as bioluminescence, chemiluminescence, photoluminescence, cathodoluminescence, electroluminescence, and electroluminescence. Fireflies, phosphors, fluorescent lamps, EL light, LED light, etc. are some typical cold light sources.
