Luminous efficiency (luminous efficiency) of LED lamps, […]
Luminous efficiency (luminous efficiency) of LED lamps, the luminous flux emitted by the light source divided by the power consumed by the light source. It is an important index to measure the energy saving of light source.
Luminous efficiency is the parameter of a light source, which is the ratio of luminous flux to power. Depending on the situation, this power can refer to the radiation flux output by the light source, or the energy (electrical energy, chemical energy, etc.) provided by the light source. The power in luminous efficiency usually depends on the situation, but in many cases the reference is unknown.
Because of the structure of the human eye, not all wavelengths have the same visibility. The spectra of infrared and ultraviolet light have no effect on the luminous efficiency. The luminous efficiency of light source is related to the ability of light source to convert energy into electromagnetic radiation and the ability of human eyes to perceive the radiation.
Luminous flux refers to the radiation power that the human eye can feel. It is equal to the product of the radiation energy of a certain band and the relative visibility of that band in unit time. Because the relative visibility of human eyes to different wavelengths of light is different, when the radiation power of different wavelengths of light is equal, the light flux is not equal.
Luminous flux refers to the derived quantity of radiation flux evaluated according to the international standard human visual characteristics, which is represented by symbol Φ (or Φ R). The unit of luminous flux is LM (lumen). 1lm is equal to the luminous flux emitted by a point light source with uniform luminous intensity of 1CD (candela) in 1sr (sphericity) unit solid angle, that is, 1lm = 1CD · Sr.
The nominal luminous flux of a 40W incandescent lamp is 360lm, that of a 40W fluorescent lamp is 2100lm, and that of a 400W standard high pressure sodium lamp is 48000lm.
Luminous efficiency brightness:
Brightness refers to the physical quantity of the intensity of light (reflection) on the surface of the illuminant (reflector). The ratio of the light intensity in this direction to the light source area "seen" by the human eye is defined as the luminance of the light source unit, that is, the luminous intensity of the unit projection area. Luminance is indicated by the symbol L, and the unit of luminance is candela / square meter (CD / m2).
The brightness of the light source is related to the surface area of the luminescent body. Under the same light intensity, if the luminescent area is large, it will be dark, otherwise it will be bright.
The brightness is also related to the direction of the light-emitting surface. The brightness values of the same light-emitting surface are different in different directions, usually measured in the direction perpendicular to the line of sight.
For example, in common lighting, if you want to reduce the brightness of the subject, especially the face of the person, the normal way is to pull the distance of the lamp a little longer, or add soft light paper in front of the lamp to reduce the intensity of the light.