LED light emitting principle, structure, product classification and summary

Time:2018-11-29 Views:137

I. LED light emitting principle and structure

The basic knowledge that semiconductor materials can produce light was known 50 years ago, and the first commercial diode was produced in 1960.LED (lightemittingdiode) is the abbreviation of the basic structure is an electroluminescent semiconductor material, placed on a lead rack, and then all around with epoxy resin seal, play a role in protecting the internal core wire, so LED should be able to resist earthquake.

The core of led is a chip composed of p-type semiconductor and n-type semiconductor. There is a transition layer between p-type semiconductor and n-type semiconductor, which is called p-n junction.In PN junction of some semiconductor materials, the combination of minority carriers and majority carriers injected will release the excess energy in the form of light, thus directly converting electrical energy into light energy.PN junction plus reverse voltage, a few carriers are difficult to inject, so no light.This kind of diode that USES injection electroluminescence principle to make is called LED, common name LED.When it is in a positive working state (that is, add a positive voltage at both ends), when the current flows from the LED anode to the cathode, the semiconductor crystal will emit different colors of light from ultraviolet to infrared, and the intensity of light depends on the current.

Ii. Characteristics of LED light source

1. Voltage: LED USES low-voltage power supply, the supply voltage is between 6-24v, depending on the product, so it is a safer power supply than using high-voltage power supply, especially suitable for public places.

2. Efficiency: the energy consumption is 80% lower than that of incandescent lamps with the same light effect

3. Applicability: very small, each unit LED chip is 3-5mm square, so it can be prepared into various shapes of devices, and suitable for the changeable environment

4. Stability: 100,000 hours, 50% of the initial light fade

5. Response time: the response time of the incandescent lamp is millisecond, and that of the LED lamp is nanosecond

6. Environmental pollution: no harmful metal mercury

7. Color: changing the current can change the color. Led can easily adjust the band structure and band gap of the material through chemical modification, so as to achieve multi-color luminescence of red, yellow, green, blue, blue and orange.For example, if the LED is red when the current is small, it can change to orange, yellow and green successively with the increase of current

8. Price: leds are relatively expensive. Compared with incandescent lamps, several leds can cost as much as one incandescent lamp.

Iii. Types and development history of monochromatic LED

The LED light source made of semiconductor p-n junction luminescence principle first appeared in the early 1960s.The material used was GaAsP, or glowing red lambda p=650nm. At 20 ma, the luminous flux is only a few thousandths of a lumen, or about 0.1 lumen/watt.

In the mid-1970s, elements In and N were introduced to produce green light (lambda p=555nm), yellow light (lambda p=590nm) or orange light (lambda p=610nm) for leds, or lambda p=610nm, with a light efficiency of 1 lumen/watt.

By the early 1980s, GaAlAs‘s LED light sources had emerged, enabling red leds to achieve a light efficiency of 10 lumens per watt.In the early 1990s, GaAlInP, which emits red and yellow light, and GaInN, which emits green and blue light, were successfully developed, resulting in substantial improvement in LED light efficiency.In 2000, the former had a light efficiency of 100 lumens per watt for the red or orange area of lambda p=615nm, or the latter had a light efficiency of 50 lumens per watt for the green area of lambda p=530nm.

Iv. Application of monochromatic LED

LED was originally used as the indicator light source of instruments and meters. Later, LED of various light colors was widely used in traffic signal lights and large-area display screens, which produced good economic and social benefits.Take 12-inch red traffic lights. In the United States, 140-watt incandescent lamps with long life and low light efficiency were originally used as the light source, which produced 2,000 lumens of white light.Through the red filter, 90% of the light is lost, leaving only 200 lumens of red light.In the new design, Lumileds USES 18 red LED lights that use 14 watts of electricity, including circuit losses, to achieve the same luminous effect.

The automobile signal light is also the LED light source application important domain.In 1987, China began to install high brake lights on cars, because the LED response speed is fast (nanosecond level), can let the driver following the vehicle know the driving condition as early as possible, reduce the occurrence of rear-end accidents.In addition, LED lights in the outdoor red, green, blue full-color display, keychain type micro flashlight and other fields have been applied.

V. development of white LED

To general illume character, people needs white illuminant more.In 1998, white LED was successfully developed.The LED is a GaN chip and yttrium aluminum garnet (YAG) encapsulated together to make.GaN chip is blue light emitting (lambda p=465nm, Wd=30nm), which is fired by high-temperature sintered YAG phosphor containing Ce3+ with a peak value of 550nm.The blue LED substrate is installed in a bowl-shaped reflector cavity and covered with a thin layer of resin mixed with YAG, about 200-500nm.Part of the blue light emitted by the LED substrate is absorbed by phosphors, while the other part is mixed with the yellow light emitted by phosphors to obtain white light.Now, for InGaN/YAG white LED, white light with color temperature of 3500-10000k can be obtained by changing the chemical composition of YAG phosphor powder and adjusting the thickness of phosphor powder layer.