Why do We Need Light

Light is very important to the survival and development of human beings. After the baby birth， the first impression the baby comes into contact with the nature is light. Light is a tool for human beings to know the world. About 90% of external information received by the human senses is sent to the brain through eyes. With light， human beings can see the colorful world. Nevertheless， most often people may not realize that light is all around us， and that it is changing the way we live. Because human eyes can see only the visible light which is only a small part of the whole spectrum， but be blind to a lot of infrared light， ultraviolet light and X-ray. At the same time， light-based technologies also play a crucial role behind the scenes.

Light and light-based technologies are an important driving force for modern technology and social productivity. Applications of light-based technologies in some important fields are introduced below.

Light plays an important role in generation， modulation， transmission， storage， display and processing of information， and the importance of fiber optic communication is self-evident. Light quantum communication based on quantization of light is more secure and confidential. IMAX 3D cinema， high-definition three-dimensional television， iris mobile phone display and other advanced equipment bring people with stunning viewing experience. Photoelectric detection instruments， optical remote sensing & remote control instruments， robot vision， optical sensors， optical disc storage， etc. give full play in various fields.

On many occasions， we can detect via X-rays， terahertz light， etc. whether firearms， ammunition， flammable and combustibles， corrosives， toxic and radioactive substances， drugs and other dangerous and prohibited items are carried. Visible light is very weak at night， while there are abundant infrared rays that human eyes cannot see， infrared viewing device can help people observe， search， target and drive vehicles. Laser ranging is the extension of radar ranging principle to optical frequencies so that human beings can measure the distance from the earth to the moon in centimeter. Because it can quickly and accurately measure the target distance， it is widely used in reconnaissance measurement and weapon fire control system. Laser gyro is widely used in high-precision inertial navigation in the field of aviation， spaceflight， navigation， etc.， and has high angular displacement measurement precision and wide range of measured angles without error caused by the friction of mechanical moving parts. When a laser guided weapon attacks a fixed or moving target， it has precision of less than 1m and high hit rate just like it has eyes. Tactical laser weapons made of high-power lasers can make human eyes blind and disable photodetectors. Tactical laser weapons made of high-energy laser beams can instantly destroy aircraft， missiles， satellites and other military targets， and are real "death rays" frightening enemies.

The vast majority of energy sources providing energy for human beings directly or indirectly come from the sun. Plants convert the solar energy into chemical energy through photosynthesis and store it. Coal， petroleum， natural gas and other fossil fuels are also formed by animals and plants buried underground after a long geological time， which are essentially the solar energy formed by the settlement of ancient creatures. In addition， water power， wind energy， etc. are also converted by the solar energy. Due to limited storage capacity of fossil energy， direct use of solar energy instead of fossil fuels is becoming increasingly important today. Solar energy is an inexhaustible， renewable and clean energy， therefore， photovoltaic power generation （sunlight directly converts into electricity） is developing rapidly in recent years. At the same time， reducing energy consumption is also important. From incandescent lamp to fluorescent lamp， and to semiconductor diode， the lighting quality is getting higher， but the energy consumption is getting less. Development of green lighting is of great significance for saving the earth's limited resources.

Light is the origin of life， and optical technologies have been applied to the origin of life， physical examination， medical treatment， and other areas. After the discovery， X-ray has been applied to medical imaging just within a few months. Discovery of DNA double helix model with X-ray diffraction emblemizes that medical research enters a new field. Protein structure analysis relies on X-ray diffraction. Fluorescence recovery after photo bleaching， laser diffraction measurement technology， laser flow cytometry， laser Raman spectroscopy and other advanced technologies can measure molecular structures or constituents in the cells. In medical treatment， shadow less lamp， laser scalpel， laser therapy apparatus， laser micro beam technology， endoscopic laser， photodynamic therapy， etc. have been widely used in various clinical branches.

Laser processing can realize high-precision cutting， welding， surface treatment， boring， and micromachining. The advanced manufacturing technology has been widely used in important sectors of national economy， such as automotive， electronics， appliances， aviation， metallurgy， machinery manufacturing， and plays an increasingly important role in improving product quality， labor productivity， automatization， no pollution， and reducing material consumption， etc. Laser cutting is used to cut titanium alloy used in automobile industry， computers， electrical cabinets， and aerospace industry. Laser welding is used when welding thick and thin plates of automobile body， auto part， lithium battery， cardiac pacemaker， sealed relay and other sealing devices as well as the devices which allow no welding contamination and deformation. Laser processing technology has greatly improved mechanical properties， heat resistance and corrosion resistance， etc. of materials. Laser marking technology has been widely used in various materials and almost all industries. Laser boring is mainly used in aerospace， automobile manufacturing， electronic instrument， chemical industry and other industries. Laser rapid prototyping is a new technology integrating laser processing technology with computer numerical control technology and flexible manufacturing technology. Laser 3D printing technology has been developing rapidly in recent years.

In short， light and light-based technologies have had a profound impact on human survival， global economy， social development and national security. With the further development， light and light-based technologies will continue to change human's prodution， living and cognitive styles. And the world will become better because of light！