1. Basic optical definitions and units:
Solid angle: The angle formed by an area on a sphere relative to its center is called a solid angle. The unit of solid angle is Sr (radian). The relative solid angle of the entire sphere is 4π.
Luminous flux: The energy radiated by a light source to the surrounding space in unit time and causing vision is called luminous flux, represented by the symbol Φ. The unit is lumen lm. It is mainly used to describe the overall performance of a light source or a light beam.
Illuminance: Illuminance is used to indicate the light intensity on the illuminated surface (point). The ratio of luminous flux to the illuminated surface area is called surface illuminance. I will use the symbol E, and the unit is lux.
Optical performance indicators are mainly used for lighting functions.
Luminous intensity: The luminous flux radiated by a light source in a certain direction of space per unit solid angle is called the luminous intensity of the light source in that direction. I will use the symbol I, candela CD.
Mainly used for optical performance indicators of signal lights.
Brightness: Brightness refers to the intensity of the physical quantity of light (reflector) on the surface of a light body (reflector). The human eye observes the light source from one direction, and the ratio of the light intensity in that direction to the area of the light source "seen" by the human eye is defined as the unit brightness of the light source, that is, the luminous intensity per unit projection area. Unit: nitrate (CD/m2)
Light source efficiency:
Light efficiency refers to the efficiency of converting electrical energy into light energy. Unit: lumen/watt lm/W
2. Color rendering:
In principle, artificial light should be the same as natural light, allowing the human eye to correctly distinguish the color of things, of course, depending on the location and purpose of the lighting. The degree to which a light source presents the color of an object is called color rendering. It is often referred to as the "color rendering index" (RA).
Color rendering refers to the relationship between the true color (own color) of an object and the color displayed under a standard light source. The Ra value is determined by comparing the 8 test colors defined in the DIN6169 standard with the standard light source to be tested. The smaller the color difference, the better the color rendering effect of the light source being tested. A light source with an Ra value of 100 means that the color of an object under its light is the same as the color under a standard light source.
3. Color temperature:
A dark red light, when a black object is heated to a certain temperature, it starts to glow, and at higher temperatures the color changes to yellowish white/white/bluish white. When an object emits light of a certain color, we call its temperature the color temperature of that color.
