第 1 部分：什么是光？
Part 1: What is Light?

光的概念
The concept of light

光是一个物理学名词，其本质是一种处于特定频段的光子流。光源发出光，是因为光源中电子获得额外能量。如果能量不足以使其跃迁到更外层的轨道，电子就会进行加速运动，并以波的形式释放能量。如果跃迁之后刚好填补了所在轨道的空位，从激发态到达稳定态，电子就停止跃迁。否则电子会再次跃迁回之前的轨道，并且以波的形式释放能量。
Light is a physical term whose essence is a stream of photons in a specific frequency band. A light source emits light because the electrons in the light source gain extra energy. If the energy is not enough to make it jump to a more outer orbit, the electrons undergo an accelerated motion and release the energy in the form of a wave. If the transition is followed by just enough to fill the vacancy in the orbit and go from the excited state to the stable state, the electron stops transitioning. Otherwise, the electrons jump back to their previous orbits again and the energy is released in the form of waves.

第 2 部分：什么是光源？
Part 2: What is a Light Source?
正在发光的物体叫光源，正在这个条件必须具备，光源可以是天然的或人造的。物理学上指能发出一定波长范围的电磁波（包括可见光与紫外线、红外线、X射线等不可见光）的物体。
The object that is emitting light is called a light source, and it must be in this condition, and the light source can be natural or artificial. In physics, it refers to an object that can emit electromagnetic waves in a certain wavelength range (including visible light, ultraviolet, infrared, X-rays and other invisible light).
光源主要可以分为三类。
There are three main types of light sources.

第一类是热效应产生的光。太阳光就是很好的例子，因为周围环境比太阳温度低，为了达到热平衡，太阳会一直以电磁波的形式释放能量，直到周围的温度和它一样。
The first category is the light produced by the thermal effect. Sunlight is a good example because the surroundings are cooler than the sun, and in order to achieve thermal equilibrium, the sun releases energy in the form of electromagnetic waves until the surrounding temperature is the same as it.
第二类是原子跃迁发光。荧光灯灯管内壁涂抹的荧光物质被电磁波能量激发而产生光。此外霓虹灯的原理也是一样。原子发光具有独自的特征谱线。科学家经常利用这个原理鉴别元素种类。
The second type is atomic transition luminescence. The fluorescent substance applied to the inner wall of the fluorescent lamp tube is excited by the energy of electromagnetic waves to produce light. In addition, the principle of neon is the same. Atomic luminescence has its own characteristic spectral lines. Scientists often use this principle to identify elemental species.
第三类是物质内部带电粒子加速运动时所产生的光。譬如，同步加速器工作时发出的同步辐射光，同时携带有强大的能量。
The third type is the light produced when the charged particles inside the substance are moving at an accelerated pace. For example, synchrotron radiation emitted by a synchronous accelerator also carries a lot of energy.

第 3 部分：什么是光子？
Part 3: What is a Photon?
根据量子场论（或者量子电动力学），光子是电磁场量子化之后的直接结果。光的粒子性揭示了电磁场作为一种物质，是与分子、原子等实物粒子一样，有其内在的基本结构（组成粒子）的。
According to quantum field theory (or quantum electrodynamics), photons are the direct result of the quantization of electromagnetic fields. The particle nature of light reveals that the electromagnetic field, as a substance, has an intrinsic basic structure (constituent particles) like physical particles such as molecules and atoms.

第 4 部分：世界上最快的速度------光速。
Part 4: The World's Fastest Speed ------ the Speed of Light.
通常指电磁波（包括光波）在真空中传播的速率，常用c表示。实验测得各种波长的电磁波在真空中的速度是一常数，其值为c=2.99792458×108米/秒 [3]。
It usually refers to the rate at which electromagnetic waves (including light waves) propagate in a vacuum, and is often denoted by C. The velocity of electromagnetic waves of various wavelengths in a vacuum is a constant with a value of c = 2.99792458×108 m/s [3].

第 5 部分：光研究的历史。
Part 5: History of Light Research.

光的研究历史和力学一样，在古希腊时代就受到注意，光的反射定律早在欧几里得时代已经闻名，但在自然科学与宗教分离开之前，人类对于光的本质的理解几乎再没有进步，只是停留在对光的传播、运用等形式上的理解层面。 （ 另，历史告诉我们，古中国早在战国初期，墨学创始人墨子便发现了光的反射定律，建立了中国的光学体系。）十七世纪，对这个问题已经开始存在波动学说和粒子学说两种声音。1925年，法国物理学家德布罗意又提出所有物质都具有波粒二象性的东西的理论，即认为所有的物体都既是波又是粒子，随后德国著名物理学家普朗克等数位科学家建立了量子物理学说，将人类对物质属性的理解完全展拓了。综上所述，光的本质应该认为是光子，它具有波粒二象性。
The history of the study of light, like mechanics, has been noted in the ancient Greek era, and the law of reflection of light has been known as early as the time of Euclid, but before the separation of natural science and religion, human understanding of the nature of light has hardly improved, and it only stays at the level of understanding of the propagation and application of light.   (In addition, history tells us that as early as the early Warring States period in ancient China, Mozi, the founder of Moxue, discovered the law of reflection of light and established China's optical system. In the seventeenth century, there were already two voices on this issue: the wave theory and the particle theory. In 1925, the French physicist de Broglie put forward the theory that all matter has wave-particle duality, that is, all objects are both waves and particles, and then the famous German physicist Planckand other scientists established the theory of quantum physics, which completely expanded the understanding of human beings on the properties of matter. To sum up, the essence of light should be considered as photons, which have wave-particle duality.

第 6 部分：光具备的五个重要特征：
Part 6: Five Important Characteristics of Light:

1 在几何光学中，光以直线传播。
 1 In geometric optics, light travels in a straight line.
2 在波动光学中，光以波的形式传播。不同波长的光呈现不同的颜色。

2 In wave optics, light travels in the form of waves. Different wavelengths of light exhibit different colors.
3 光速极快。在真空中为299792458≈3×10⁸m/s，

3 The speed of light is extremely fast. 299792458≈3×10⁸m/s in vacuum
4 在量子光学中，光的能量是量子化的，构成光的量子（基本微粒），我们称其为光量子，简称光子，因此能引起胶片感光乳剂等物质的化学变化。

4 In quantum optics, the energy of light is quantized, and the quanta (elementary particles) that make up light, we call them light quanta, or photons for short, so they can cause chemical changes in substances such as film photosensitive emulsions.
5 光的偏振：光的偏振现象有别与光的其它性质，人的感觉器官不能感觉偏振的存在。偏振光可分为部分偏振光、线偏振光（平面偏振光）、椭圆偏振光和圆偏振光。

5 Polarization of light: The polarization phenomenon of light is different from other properties of light, and the human sensory organs cannot sense the existence of polarization. Polarized light can be divided into partially polarized light, linearly polarized light (planar polarized light), elliptically polarized light, and circularly polarized light.

第 7 部分：光是如何传播的？
Part 7: How Does Light Travel?
光在同种均匀介质中沿直线传播。小孔成像、日食和月食还有影子的形成都证明了这一事实。
Light travels in a straight line in the same homogeneous medium. Aperture imaging, solar and lunar eclipses, and the formation of shadows all testify to this fact.
在几何光学中，以一条有箭头的几何线代表光的传播方向，叫做光线。
In geometrical optics, a geometric line with an arrow represents the direction of light propagation, which is called light.
几何光学中光的传播规律有三：
There are three laws of light propagation in geometric optics:
（1）光的直线传播规律。
(1) The law of linear propagation of light.

（2）光的独立传播规律。
(2) The law of independent propagation of light.

（3）光的反射和折射定律。
(3) The law of reflection and refraction of light.

光传播途中遇到两种不同介质的分界面时，一部分反射，一部分折射。
When light travels through the interface of two different media, part of it is reflected and part of it is refracted.
反射光线遵循反射定律，折射光线遵循折射定律。
Reflected rays follow the law of reflection, and refracted rays follow the law of refraction.

第 8 部分：光的应用。
Part 8: Application of Light.
光在能源（清洁能源：太阳能）、电子（电脑、电视、投影仪、摄像机、扫描仪）、通信（光纤）、医疗保健（γ光刀、光波房、光波发汗房、X光机）、研究（显微镜、放大镜、望远镜）、交通（红绿灯、路灯、霓虹灯）等方面有广泛的应用。
Light in energy (clean energy: solar energy), electronics (computers, etc.). TVs, projectors, cameras, scanners), communications (fiber optics), health care (γ light knife, light wave room, light wave sweat room, X-ray machine), It has a wide range of applications in research (microscopes, magnifying glasses, telescopes), traffic (traffic lights, street lights, neon signs), etc.

第 9 部分：三个小问题。
Part 9: Three Little Questions.

1：光是什么？
1: What is light?

答案：光是一个物理学名词，其本质是一种处于特定频段的光子流。
Answer: Light is a physical term whose essence is a stream of photons in a specific frequency band.

2：光在哪方面有应用？（说出三方面并分别举例即可）
2: In what ways does light have applications? (Just name the three and give examples of each one).

答案：光在能源（清洁能源：太阳能）、电子（电脑、电视、投影仪、摄像机、扫描仪）、通信（光纤）、医疗保健（γ光刀、光波房、光波发汗房、X光机）、研究（显微镜、放大镜、望远镜）、交通（红绿灯、路灯、霓虹灯）
Answer: Light in Energy (Clean Energy: Solar), Electronics (Computer, TVs, projectors, cameras, scanners), communications (optical fiber), Health care (γ light knife, light wave room, light wave sweat room, X-ray machine),Research (microscopes, magnifying glasses, telescopes), traffic (traffic lights, street lights, neon lights).

3：光的特性
3: Characteristics of light

答案：光同时具备以下五个重要特征：
Answer: Light has the following five important characteristics at the same time:

1 在几何光学中，光以直线传播。2 在波动光学中，光以波的形式传播。3 光速极快。在真空中为299792458≈3×10⁸m/s。4 在量子光学中，光的能量是量子化的。 5 光有偏振现象。
 1 In geometric optics, light travels in a straight line.  2 In wave optics, light travels in the form of waves.  3 The speed of light is extremely fast. 299792458≈3×10⁸m/s in vacuum.  4 In quantum optics, the energy of light is quantized.  5 Light is polarized.