Do You Really Understand Light?

The Essence of Light.

For centuries, there have been contradictory scientific theories about the nature of light, yet these disciplines have been complementing and continuously merging with each other.

In the 17th century, Newton proposed the corpuscular theory of light. He believed that light is composed of elastic spherical particles known as "light corpuscles." Newton posited that light consists of a stream of mechanical particles, resembling small bullets, which emit a continuous flow of high-speed, straight-line flying light particles. When these particles enter the human eye, they strike the retina, causing vision. This is the corpuscular theory of light. Based on this, Newton discovered the laws of light's straight-line propagation, reflection, and refraction.

2. The Wave Theory of Light. During the same period as Newton, Huygens (Wheegense) proposed the wave theory of light in his monograph "On Light." He believed that light propagates in the form of spherical waves. If light encounters an obstacle with a small hole during its propagation, a new spherical wave is formed behind the hole. This theory can explain the phenomena of light interference and diffraction.

3. The Electromagnetic Wave Theory. In the 19th century, Maxis proposed the electromagnetic theory of light. He believed that light is a type of electromagnetic wave propagating through space. This theory delves into the electromagnetic nature of light, highlighting the consistency between light and electromagnetic properties. It proves that X-rays, ultraviolet light, visible light, infrared radiation, and radio waves are essentially the same, differing only in their wavelengths.

4. Quantum Theory. In the early 20th century, Planck proposed the quantum theory of light. He believed that when an emitting body emits light waves, it does so in discrete packets. The light source emits one "energy particle" at a time, each with a fixed size, known as a quantum of that light. The size of a quantum is only related to the frequency of the light. According to Planck's theory, light has not only wave-like properties but also particle-like properties represented by quanta. The size of the quantum is determined by the frequency, hence the quantum of ultraviolet light is larger, followed by visible light, and the quantum of infrared light is smaller. This theory explains the thermal effect, chemical effect, fluorescence, and light pressure of light.

II. Classification of Light

Based on the wavelength of light, there are visible light and invisible light.

Visible Light: Represents a very small portion of the electromagnetic spectrum. When sunlight passes through a prism, the different wavelengths of light refract at different angles as they pass through the medium, causing the sunlight to disperse into the seven colors of red, orange, yellow, green, cyan, blue, and purple on the white screen behind the prism. The wavelength of visible light ranges from 400-780nm. (Note: 1μm = 1000nm)

Ultraviolet Light: Beyond the violet end of the spectrum lies ultraviolet light, which is invisible to the naked eye and has a wavelength of approximately 180-400nm. Ultraviolet light is divided into three bands—UVA, UVB, and UVC—based on its wavelength, each with different application ranges. Due to the germicidal effect of the UVC band of ultraviolet light on most microorganisms, bacteria, and viruses on Earth, it is widely used in air sterilization and surface disinfection, making it one of the most effective spectral sterilization methods currently available.

Beyond ultraviolet rays, there are high-energy rays such as X-rays, gamma rays, and cosmic rays.

3. Infrared: Beyond the red end of the spectrum lies infrared, which is also invisible light, with wavelengths ranging from 780 to 10,000 nm. Similarly, infrared light is categorized into three types based on its wavelength range: long-wavelength (IR-C), medium-wavelength (IR-B), and short-wavelength infrared (IR-A). Infrared possesses significant thermal radiation benefits and is widely used in the heating field in modern production.