Deep analysis of LED terminology and the secret of LED life

Why is the life of LEDs long?

That is to start from the principle of LED lighting. LED (Light Emitting Diode), which is a light emitting diode. It is a semi-conductive solid state light emitting device. It uses a solid semiconductor chip as a luminescent material. When a forward voltage is applied to both ends, red, yellow, green, cyan, orange, purple, and white light are directly emitted. Many changes: LED light source can use LED short-time short and red, green, blue three primary color principle, under the control of computer technology to achieve multiple changes in color and pattern, is a kind of "dynamic light source" that can be controlled at will.

The illuminating mechanism of incandescent lamps is that electric energy heats and emits luminescent tungsten wires. After a long period of heating, the tungsten wires will age or even burn out. At this point, the life of incandescent bulbs ends, and the luminescence mechanism of LEDs ends. It is determined by the special composition of the diode. The diode is mainly composed of a PN junction chip, an electrode and an optical system. When a forward bias is applied to the electrode, electrons and holes are injected into the P region and the N region, respectively. When the balance of minority carriers and majority carriers is balanced, excess energy is converted into light energy in the form of radiated photons. The illuminating process consists of three parts: carrier injection under forward bias, composite radiation, and light energy transmission.

It can be seen that the diode mainly emits light by the continuous movement of carriers, and there is no aging and burning phenomenon. Its special light-emitting mechanism determines its luminous lifetime of up to 50,000-100,000 hours.

LED terminology

LED terminology mainly includes: luminous flux/luminous intensity/luminance/illuminance.

The luminous flux is an index indicating the overall brightness of the light source. The unit is lm (lumen). It is often used when indicating the brightness of the illumination source. It is a reference to the sensitivity (visual sensitivity) of the human eye to indicate the physical quantity of the light emitted by the light source. The specific value is that the light flux of the isotropic light source having a luminous intensity of 1 cd (candela) is 1 lm in a solid angle of 1 sr (stereo radiance). Here, sr is a unit of a solid angle, and indicates an apex angle of a cone whose area taken from the ball toward the center of the sphere is the radius 2 (r[size=+0]2).

Light intensity is an indicator of the solid angular density of light flux. The unit is cd. It is often used when indicating glare of a display LED or the like. It is defined as: a 540×1012 Hz (wavelength 555 nm) frequency monochromatic light is emitted, and a light source having a intensity of 1/683 W/sr is emitted in a specified direction, and the light intensity in this direction is defined as 1 cd.

The brightness is an index indicating the intensity of light emitted from the secondary light source such as the light source and the reflecting surface and the transmitting surface to the observer. The unit is cd/m2. Like the luminous flux, it is a physical quantity expressed in combination with the sensitivity of the human eye. Most of them are used when indicating the brightness of a display screen such as a liquid crystal panel or a PDP.

Illuminance is an indicator of the brightness of light that is incident on a plane. The unit is lx (lux) and is sometimes labeled lm/m2. It refers to the luminous flux per unit area of ​​the luminous flux of the light source that is directed toward the planar object. Led is brighter than the lighting fixture on the plane.

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