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The LED is an abbreviation taken from the three words of LightEmittingDiode, which is translated into "light-emitting diode" in Chinese. As the name suggests, a light-emitting diode is a diode that can convert electrical energy into light energy. At present, different light-emitting diodes can emit light of different wavelengths from infrared to blue, and light-emitting diodes that emit purple or ultraviolet light have also been born. In addition to this, there are white LEDs that are coated with phosphors on blue LEDs to convert blue light into white light.
The color and process of LEDs: Different materials for LEDs can produce photons with different energies, which can control the wavelength of the light emitted by the LED, that is, the spectrum or color. The material used in the history of the first LED is arsenic (As) gallium (Ga), its forward PN junction voltage drop (VF, can be understood as Lighting or operating voltage) is 1.424V, the emitted light is infrared spectrum . Another commonly used LED material is phosphorous (P) gallium (Ga), which has a forward PN junction voltage drop of 2.261V and emits green light.
Based on these two materials, the early LED industry used the GaAs1-xPx material structure to theoretically produce LEDs from infrared light to any wavelength in the green range. The subscript X represents the percentage of phosphorus replaced by arsenic. The wavelength of the LED is typically determined by the PN junction voltage drop. Typical of these are red LEDs with GaAs 0.6P0.4, orange LEDs with GaAs 0.35P0.65, and ?S LEDs with GaAs 0.14P0.86. Since the manufacturing uses three elements of arsenic, arsenic and phosphorus, these LEDs are commonly referred to as three-element luminous tubes. The GaN (gallium nitride) blue LED, the GaP green LED, and the GaAs infrared LED are called two-element LEDs. The latest technology is a four-element LED made of four-element AlGaInN mixed with aluminum (Al), calcium (Ca), indium (In) and nitrogen (N) elements, covering all visible light and some UV. The spectral range of light.
LED luminous intensity:
Luminous intensity is measured in units of illuminance (Lux Lux), Luminous Flux units (Lumen Lumen), Luminous Intensity Units (Candlelight Candlepower)
1CD (candle light) refers to the luminous intensity of a completely radiated object at an area of ​​one-sixth of a square centimeter at the freezing point of platinum. (Formerly a whale oil candle with a diameter of 2.2 cm and a mass of 75.5 grams, burning 7.78 grams per hour, a flame height of 4.5 cm, luminous intensity along the horizontal direction)
1L (lumen) refers to the luminous flux of a 1CD candle light on a plane with a distance of 1 cm and an area of ​​1 cm 2 .
1Lux refers to the illuminance of 1L of luminous flux evenly distributed over an area of ​​1 square meter.
Generally, the active illuminator adopts a luminous intensity unit candle CD, such as an incandescent lamp, an LED, etc.; a reflective or penetrating object uses a luminous flux unit lumen L, such as an LCD projector, and the illuminance unit Lux Lux, which is generally used in photography and the like. . The three units of measure are numerically equivalent, but need to be understood from different angles. For example, if the brightness (light flux) of an LCD projector is 1600 lumens, and the size of the projection to the total reflection screen is 60 inches (1 square meter), the illumination is 1600 lux, assuming that the light exits from the light source 1 In centimeters, the area of ​​the light exit is 1 square centimeter, and the luminous intensity of the light exit is 1600CD. The true LCD projector, due to loss of light propagation, loss of reflection or light-transmissive film, and uneven distribution of light, will greatly reduce the brightness, and generally 50% efficiency is very good.
In actual use, light intensity calculations often use data units that are easier to map or use. For the LED display screen, the active illuminant generally adopts CD/m2 as the unit of luminous intensity, and the observation angle is used as an auxiliary parameter, which is equivalent to the illuminance unit of the screen surface; this value and the effective display area of ​​the screen Multiply, the illuminance of the entire screen at the optimal viewing angle is obtained. Assuming that the illuminance of each pixel in the screen is constant within the corresponding space, this value can be considered as the luminous flux of the entire screen. Generally, the outdoor LED display must have a brightness of more than 4000CD/m2 to have an ideal display effect under daylight. Ordinary indoor LED, the maximum brightness is about 700 ~ 2000CD / square meter.
The luminous intensity of a single LED is in units of CD: it is also equipped with a viewing angle parameter, and the luminous intensity has nothing to do with the color of the LED. The luminous intensity of a single tube varies from a few mCD to five thousand mCD. The luminous intensity given by the LED manufacturer refers to the point at which the LED illuminates at a current of 20 mA, with the highest luminous intensity at the best viewing angle and at the center position. The shape of the top lens and the position of the LED chip from the top lens when packaging the LED determine the LED viewing angle and intensity distribution. Generally speaking, the larger the LED viewing angle is, the smaller the maximum luminous intensity is, but the luminous flux accumulated on the entire three-dimensional hemisphere is unchanged.
When a plurality of LEDs are relatively tightly discharged, the illuminating spheres are superimposed on each other, resulting in a relatively uniform distribution of luminous intensity of the entire illuminating plane. When calculating the luminous intensity of the display screen, it is necessary to multiply the maximum point luminous intensity value provided by the manufacturer by 30% to 90% according to the LED viewing angle and the emission density of the LED as the average luminous intensity of the single tube.
The luminous life of LEDs is very long: manufacturers generally indicate more than 100,000 hours. Actually, attention should also be paid to the brightness decay period of LEDs. For example, most of the UR red tubes used for automobile taillights are illuminated for ten to several tens of hours, and the brightness is Only half of the original. The brightness decay period has a lot to do with the material process of LED production. Generally, when the economic conditions permit, a four-element LED with slower luminance attenuation should be selected.
Color matching, white balance: white is a mixture of red, green and blue colors according to the brightness ratio. When the brightness of green light is 69%, the brightness of red is 21%, and the brightness of blue is 10%, the human eye feels after mixing. It is pure white. However, the chromaticity coordinates of the LED red, green and blue colors cannot achieve the full chromatographic effect due to the process and the like, and the control primary colors include the brightness of the biased primary colors to obtain white light, which is called color matching.
Before color matching for a full-color LED display, in order to achieve the best brightness and the lowest cost, LED devices with three primary colors with a luminous intensity of approximately 3:6:1 should be selected to form pixels.
White balance requires that the three primary colors are still pure white synthesized at the same gray value.
Primary color, primary color: Primary color refers to the basic color that can synthesize various colors. The primary colors in the shade are red, green, and blue. The lower graph is the spectrum table. The three vertices in the table are the ideal primary wavelengths. If there is a deviation in the primary colors, the area where the color can be synthesized will be reduced, and the triangles in the spectrum table will be reduced. From a visual point of view, the color will not only be biased, but also the degree of richness will be reduced.
The red, green and blue light lines emitted by the LED are roughly classified into purple red, pure red, orange red, orange, orange yellow, yellow, yellow green, pure green, emerald green, blue green, pure blue, blue purple, etc. according to their different wavelength characteristics. Yellow, green, blue and purple are much cheaper than pure red, pure green and pure blue. Green is the most important of the three primary colors, because green occupies 69% of the brightness in white and is at the center of the color horizontal row list. Therefore, when weighing the relationship between color purity and price, green is an important consideration. 
December 15, 2023