1、 Basic Overview of Lighting
Definition of Light
Light is the part of the spectrum that can be seen by the naked eye when electromagnetic waves radiate to the human eye and are converted into light through the visual nerves. The wavelength range of such rays is between 380-780nm, which is only a very small part of the electromagnetic radiation spectrum.
PS: Many schools have an optical major, what is the difference between this major and the electrical light source major? In short, optics deals with interferometric light, while electric light sources study non interferometric light. When it comes to lighting, we must talk about the following basic concepts.
1. Luminous flux ф 
Unit: lumens (lm)
Definition: The magnitude of light radiation energy per unit time. Luminous flux is the fundamental quantity that indicates the luminous ability of a light source
Note: Luminous flux is used to measure a light source. Simply put, if the light source is a country, then the luminous flux is the GDP of that country.
2. Light intensity I
Unit: Candela (CD)
Definition: The luminous flux emitted by visible light within a specific solid angle is called luminous intensity (luminous intensity) Luminescence intensity is commonly used to indicate the distribution density of the luminous flux emitted by light sources and lamps in various spatial directions or in selected directions.
Note: Light intensity is used to represent the spatial distribution of the light output of a light source. Continuing the analogy of luminous flux mentioned above, luminous intensity actually refers to the investment intensity of a country's GDP in different regions.
3. Illuminance E
Unit: Lux (lx)
Definition: Illuminance is the ratio of the luminous flux and area of a luminous body on the illuminated plane. Illuminance is used to indicate the intensity of light on the illuminated surface.
Note: Illuminance is used to represent the average density of light output on the illuminated plane (note: not the light source). So, it's easy to understand that illuminance is the per capita income of a country's investment in a region. Note that per capita is an average concept. At this point, it is entirely possible to analogize the concept of uniformity and Gini coefficient when measuring lighting quality.
4. Brightness L
Unit: nits, i.e. candela per square meter (CD/M)
Definition: Brightness is the ratio of the light intensity observed by the human eye from one direction to the area of the light source seen by the human eye. It is defined as the brightness per unit of the light source, that is, the luminous intensity per unit of projected area.
Note: Brightness measures the amount of light emitted, which can be a light source or a secondary reflective surface (such as a road surface). Here, we need to make a special comparison and explanation of the illuminance and brightness of the road surface. The illuminance of the road surface measures the amount of light input received by the road surface, while the brightness of the road surface measures the amount of light emitted by the road surface. So the brightness of the road surface actually depends on the brightness, but because illuminance is easier to measure than brightness, national standards such as illuminance measure brightness. However, we need to recognize that the brightness of the road surface is not only related to illuminance, but also to materials such as reflectance.
2、 Explanation of Lighting Professional Terminology and Terminology
Lighting technology, like any other technology or scientific discipline, has its own proprietary terminology. These special terms and concepts are used to define the characteristics of lamps and luminaires and to standardize the measurement units. Here are some important lighting terms.
1. Light
Light is an electromagnetic wave.
Visible light: A portion of the radiation energy emitted by a light source that can produce visual radiation. It is often referred to as "visible light".
Wavelength of visible light: from 380nm to 780nm
The wavelength of ultraviolet radiation: from 100nm to 380nm, invisible to the naked eye.
Infrared wavelength: From 780nm to 1mm, invisible to the naked eye.
2. Color temperature
Expressed in absolute temperature K. When a standard blackbody is heated to a certain temperature, its color gradually changes from red to light red, orange yellow, white, blue white, and blue. Using this characteristic of color change, when the color of a light source is the same as that of a blackbody at a certain temperature, we refer to the absolute temperature of the blackbody at that time as the relevant color temperature of the light source.
3. Color rendering index (Ra)
A parameter that measures the ability of a light source to display the true color of the illuminated object.
The higher the color rendering index (0-100), the closer the color reproduction of the light source is to the natural primary color.
4. Luminous flux (lumens Lm)
Represents the amount of light emitted by a luminous body, with lumens being the unit of luminous flux. (The more light emitted, the higher the lumen count)
5. Photoeffect
The ratio of the luminous flux produced by a light source to the electrical power consumed. Unit: lumens/watt (Lm/W)
6. Average lifespan
Also known as rated lifespan, it refers to the number of hours a batch of lights are lit until half of them are damaged and not lit.
7. Light intensity
Luminous flux within a unit solid angle unit: cd
8. Illuminance
Illuminance is used to indicate the degree of illumination on the illuminated surface (working surface), usually expressed in terms of the luminous flux received per unit area, measured in lux (lx) or lumens per square meter (lm/m2).
9. Brightness
Brightness is a physical quantity used to represent the intensity of surface luminescence (or reflection) of an object. The ratio of the luminous intensity of the object's luminous surface in the line of sight direction to the projected area of the luminous surface perpendicular to that direction is called the surface brightness of the luminous surface, measured in candela per square meter (cd/m2).
10. Luminescence efficiency
Commonly referred to as luminous efficiency, it is an optical quantity that describes the quality and economy of a light source. It reflects the amount of light flux emitted by the light source while consuming unit energy, in lumens per watt (lm/w)
11. Beam angle
It refers to the angle of the lighting of the lamp and the angle of the lamp cup. There are generally three types: 10 °, 24 °, and 38 °.
The effect produced by different beam angles
12. Color display and illumination
The color rendering index of the light source and the illuminance together determine the visual clarity of the environment. There is a balance between illuminance and color rendering index. The result obtained from extensive experiments is that lighting an office with a color rendering index Ra>90 results in a satisfaction level of appearance that is more than 25% higher than lighting an office with a low color rendering index (Ra<60).
It should be noted that for a good visual appearance, it is not feasible to reduce indoor lighting to a level that deteriorates visual function in order to save energy. It is advisable to choose light sources with the best color rendering index and high luminous efficiency, and use appropriate illuminance to achieve good visual appearance with minimal energy cost.
Color category
General color rendering index range
Examples of applicable locations
I
A
Ra ≥ 90
Color matching, color inspection, etc
B
90>Ra ≥ 80
Printing, food sorting, painting, shops, restaurants, etc
II
80>Ra ≥ 60
Mechanical and electrical assembly, surface treatment, control room, office, department store, etc
III
60>Ra ≥ 40
Mechanical processing, heat treatment, casting, etc
40>Ra ≥ 20
Warehouse, large metal warehouse, etc
13. The relationship between color temperature and illuminance level
14. Light environment
The light environment is people's psychological perception of light in a certain visual space.
A good lighting environment gives people a good visual experience, which directly affects their physical and mental health.
People should consider energy conservation while considering creating a good lighting environment. The concept of green lighting is how to reduce the release of mercury and save the limited energy that humans rely on for survival.