In the PN junction of some semiconductor materials, when the injected minority carriers recombine with the majority carriers, the excess energy will be released in the form of light, thereby directly converting electrical energy into light energy.
When a reverse voltage is applied to the PN junction, it is difficult for minority carriers to be injected, so no light is emitted. This type of diode made using the principle of injection electroluminescence is called a light-emitting diode, commonly known as LED.
LED characteristics
LED is the abbreviation of light-emitting diode (Light Emetting Diodeo). Because it has the advantages of high brightness, fast response speed, low voltage, low power consumption, vibration resistance, impact resistance, and long life, it has become the main light-emitting device for indoor and outdoor information display terminals.
LED and LED display
The luminous color and luminous efficiency of LED are related to the materials and processes used to make LEDs. Currently, red, green, and blue are widely used. Since LED has low working voltage (only 1.5-3V), can emit light actively and has a certain brightness, the brightness can be adjusted by voltage (or current), and it is impact-resistant, vibration-resistant, and has a long life (100,000 hours), there is currently no other display method that can match the LED display method in large display devices.
The display screen that puts red and green LEDs together as a pixel is called a two-color screen or a color screen; the display screen that puts red, green, and blue LED tubes together as a pixel is called a three-color screen or a full-color screen. The pixel size of indoor LED screens is generally 2-10 mm. Several LED tube cores that can produce different primary colors are often packaged into one. The pixel size of outdoor LED screens is mostly 12-26 mm. Each pixel is composed of several monochrome LEDs. The common finished product is called a pixel tube. The two-color pixel tube is generally composed of 3 red and 2 green, and the three-color pixel tube is composed of 2 red, 1 green and 1 blue.
Whether LED is used to make a monochrome, two-color or three-color screen, the brightness of each LED that constitutes the pixel to display the image must be adjustable.
The degree of fineness of the adjustment is the grayscale level of the display. The higher the grayscale level, the more delicate the displayed image, the richer the color, and the more complex the corresponding display control system.
Generally, the color transition of 256-level grayscale images is very soft, while the color transition boundary of 16-level grayscale color images is very obvious. Therefore, color LED screens are currently required to be made of 256-level grayscale.
There are several forms of LED luminous materials used in display screens:
① LED luminous lamp (or single lamp)
Generally composed of a single LED chip, a reflective bowl, a metal anode, and a metal cathode, and wrapped with an epoxy resin shell with light-transmitting and light-collecting capabilities. One or more (different color) single lamps can form a basic pixel. Due to its high brightness, it is mostly used in outdoor display screens.
② LED dot matrix module
The luminous matrix is composed of several chips and encapsulated in a plastic shell with epoxy resin. It is suitable for row and column scanning drive, easy to form a high-density display screen, and is mostly used for indoor display screens.
③ SMD LED (or SMD LED) is a solderable LED package that can be used for indoor full-color display screens. It can achieve single-point maintenance and effectively overcome the mosaic phenomenon.