LED lamp beads light-emitting diode principle and electrical parameters

LED is taken from the abbreviation of LightEmittingDiode three words, the Chinese translation is "light-emitting diode", as the name suggests, light-emitting diode is a kind of electronic device can be converted into light energy with diode characteristics. At present, different light-emitting diodes can be issued from infrared to blue between the different wavelengths of light, the current issue of purple and even ultraviolet light-emitting diodes have also been born. In addition to this there is a blue LED coated with phosphor, the blue light into white LED.  

LED color and process: The different materials used to manufacture LEDs can produce photons with different energies, which can control the wavelength of light emitted by the LED, that is, the spectrum or color. Historically, the material used for LEDs was gallium arsenide (Ga), whose forward PN junction voltage drop (VF, understood as the lighting or operating voltage) was 1.424V, and the light emitted was in the infrared spectrum. Another commonly used LED material is gallium phosphide (Ga), whose forward PN junction voltage drop is 2.261V, and the light emitted is green.

Based on these two materials, early LED industry using GaAs1-xPx material square structure, theoretically can be produced from the infrared light has been to the green light range of any wavelength of LED, the subscript X represents the percentage of phosphorus element instead of arsenic element. The wavelength color of the LED can be determined by the PN junction voltage drop in general. Typical examples are GaAs0.6P0.4 red LEDs, GaAs0.35P0.65 orange LEDs, and GaAs0.14P0.86 yellow LEDs. These LEDs are commonly referred to as three-element light-emitting tubes because they are manufactured using three elements: gallium, arsenic, and phosphorus. GaN (gallium nitride) blue LEDs, GaP green LEDs, and GaAs infrared LEDs are known as two-element light-emitting tubes. The current process is a four-element LED made of AlGaInN, a four-element material that mixes aluminum (Al), calcium (Ca), indium (In) and nitrogen (N), which can cover all visible light as well as part of the UV spectral range.  

LED luminous intensity:  

Luminous intensity is measured in units of illuminance (Lux), luminous flux (Lumen), luminous intensity units (candlepower)  

1CD (candlepower) refers to the luminous intensity of a fully radiated object, at the temperature of the freezing point of platinum, per one-sixtieth of the square centimeter area. (previously referred to 2.2 cm in diameter, the mass of 75.5 grams of whale oil candle, burning 7.78 grams per hour, the flame height of 4.5 cm, along the horizontal direction of luminous intensity)  

1L (lumens) refers to the luminous flux of 1CD candle light shining on a plane with a distance of 1 cm and an area of 1 cm2.  

1Lux (lux) refers to 1L of luminous flux uniformly distributed over an area of 1 square meter of illumination.  

Generally active luminous bodies use the luminous intensity unit candle CD, such as incandescent lamps, LEDs, etc.; reflective or penetrating objects use the luminous flux unit lumen L, such as LCD projectors, etc.; and the illuminance unit Lux Lux, generally used in areas such as photography. The three units of measurement are numerically equivalent, but need to be understood from different perspectives. For example, if the brightness (luminous flux) of an LCD projector is 1600 lumens and its projection onto a fully reflective screen is 60 inches (1 square meter), then its illuminance is 1600 lux, assuming that its light outlet is 1 cm from the light source and the area of the light outlet is 1 square centimeter, then the luminous intensity of the light outlet is 1600 CD. while a true LCD projector has a luminous intensity of 1600 CD due to the loss of light propagation, reflection The brightness of a real LCD projector will be greatly reduced due to the loss of light propagation, reflection or loss of light transmission film and uneven light distribution, generally a 50% efficiency is very good.  

In actual use, the light intensity calculation is often easier to map the data unit or variable use. For LED display such active luminous body is generally used CD / square meter as a unit of luminous intensity, and with the observation angle as an auxiliary parameter, its equivalent to the screen surface illumination unit lux; will be this value and the screen effective display area multiplied, get the whole screen body in the perspective of the luminous intensity, assuming that the luminous intensity of each pixel in the screen body is constant in the corresponding space, then this value can be considered also The luminous flux of the whole screen body. General outdoor LED display must reach more than 4000CD / square meters of brightness in order to have a more ideal display effect in the daylight. Ordinary indoor LED, large brightness in the 700 to 2000CD / square meters or so.  

The luminous intensity of a single LED in CD: while equipped with perspective parameters, luminous intensity and LED color has no relationship. The luminous intensity of a single tube ranges from a few mCD to 5,000 mCD. The luminous intensity given by the LED manufacturer refers to the point where the LED is lit at 20mA current, and the luminous intensity on the perspective and center position is large. The shape of the top lens and the position of the LED chip from the top lens when packaging LEDs determines the LED viewing angle and light intensity distribution. Generally speaking, the larger the perspective of the same LED, the greater the luminous intensity of the smaller, but the cumulative luminous flux on the entire three-dimensional hemisphere remains unchanged.  

When multiple LEDs are more closely regular discharge, their luminous spheres superimposed on each other, resulting in a more uniform distribution of luminous intensity throughout the luminous plane. In calculating the luminous intensity of the display, according to the LED perspective and LED emission density, the manufacturer provides a large point luminous intensity value multiplied by 30% to 90% ranging, as the average luminous intensity of a single tube.  

LED luminous life is very long: manufacturers are generally marked as more than 100,000 hours, the actual should also pay attention to the LED brightness decay cycle, such as most of the UR red tube for automotive taillights after a dozen to dozens of hours of lighting, the brightness is only half of the original. Brightness decay cycle and LED production material process has a lot to do with the general economic conditions should be selected in the case of economic conditions allow the brightness decay more slowly four elements LED.  

Color matching, white balance: white is a mixture of red, green and blue colors according to the brightness ratio, when the light in the green brightness of 69%, the red brightness of 21%, the blue brightness of 10%, the human eye feels pure white after mixing colors. But LED red, green and blue color coordinates due to the process and other reasons can not achieve the effect of the full color spectrum, and control the original color including the brightness of the original color with deviations to get white light, known as color matching.  

When the full-color LED display for color matching before, in order to achieve the brightness and the cost, should try to choose three primary colors luminous intensity into roughly 3:6:1 ratio of LED devices composed of pixels.  

White balance requires three primary colors in the same tonal gray value of the synthesis is still pure white.  

Primary colors, base colors: primary colors refer to the basic colors that can synthesize various colors. The primary colors in color light are red, green, and blue. The chart below shows the spectral table, and the three vertices in the table are the ideal primary color wavelengths. If the primary colors have deviations, the area where the colors can be synthesized will be reduced, the triangle in the spectral table will be reduced, and from a visual point of view, the colors will not only have deviations, but the richness will be reduced.  

LED emits red, green, blue light according to its different wavelength characteristics and is roughly divided into violet red, pure red, orange red, orange, orange-yellow, yellow, yellow-green, pure green, emerald green, blue-green, pure blue, blue-violet, orange-red, yellow-green, blue-violet than pure red, pure green, pure blue is much cheaper in price. The three primary colors green is important, because green occupies 69% of the brightness of white, and is in the center of the color horizontal arrangement table. Therefore, in weighing the relationship between the purity of color and price, green is the object of emphasis.