Analysis of the structure and working principle of white LED card lights

LED is the abbreviation of light emitting diode, which is an electric light source made of semiconductor technology. The core part of the LED is a wafer 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 P2N junction. During the forward conduction, the majority and minority carriers in the semiconductor recombine, and the released energy is emitted in the form of photons or part of the photons, and a large number of photons form a photon stream, that is, light emission. When the reverse voltage is applied to the P2N junction, it is difficult to inject minority carriers, so it does not emit light.Due to the different band gap energies of semiconductor materials, different semiconductor materials

LED is the abbreviation of light emitting diode, which is an electric light source made of semiconductor technology. The core part of the LED is a wafer 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 P2N junction. During the forward conduction, the majority and minority carriers in the semiconductor recombine, and the released energy is emitted in the form of photons or part of the photons, and a large number of photons form a photon stream, that is, light emission. When the reverse voltage is applied to the P2N junction, it is difficult to inject minority carriers, so it does not emit light. Due to the different band gap energies of semiconductor materials, LEDs of different semiconductor materials can emit light of different colors.

LED light source has the characteristics of small size, long life, low power consumption, fast reflection speed, rich colors, and flat packaging. It is an environmentally friendly and energy-saving cold light source. Due to the above characteristics of LEDs, they are widely used in Display and lighting fields.

In 1965, the first commercial LED (red light) came out with an efficiency of only 0.1 lm/W. In 1968, the efficiency of LED made of GaAsP material has reached 1 lm/W, and can emit red, orange, and yellow light. In the early 1990s, the successful development of two new materials, GaAlInP, which emits red and yellow light, and GaInN, which emits green and blue light, greatly improved the light efficiency of LEDs. In 1998, the successful development of white LEDs marked the arrival of a revolution in lighting technology.

1 The latest development of white LED

In December 2006, Japan’s Nichia Chemical Industry released a white LED with a luminous efficiency of 150 lm/W when the forward current is 20 mA. Its luminous efficiency has reached about 1.7 times that of fluorescent lamps with improved color rendering. It is incandescent. 11. 5 times that of the lamp, even surpassing the high-pressure sodium lamp, which is generally believed to have the highest luminous efficiency. Showa Denko Group (SDK) has developed a new process for manufacturing high-quality gallium nitride (GaN)-based and other nitride-based compound semiconductors, mainly for blue and white LEDs. In February 2007, Philip s Lumileds announced the LED epitaxy technology (, which basically solves the problem of white light high-power LED luminous efficiency falling with the increase of current, which can make the luminous efficiency increase with the increase of driving current. Cyberlux claims that the use of plastic materials can Make the price of white light LEDs cheaper. This technology can significantly reduce manufacturing costs, and the brightness of lighting is also better than traditional white light LEDs. In March 2007, Seoul Semiconductor (SSC) launched 35,000 hours, luminous flux of 96 lm. The angular 2 W single chip Acriche can be directly plugged into a 110 V or 220 V AC power supply without an AC/DC converter. SSC plans to increase the luminous efficiency of Ariche to 120 lm/W by 2008.

At present, the thickness of the LED chip is only 0.4 mm, and the light extraction technology of the LED has also made great progress. Therefore, backlight sources with LEDs are gradually used in small displays such as third-generation mobile phones, PDAs, portable DVDs, and digital cameras. In addition, various lights on automobiles, such as front and rear lights, side lights, headlights, interior lights and dashboard displays, will be fully developed and applied. According to the statistics of Strategies Un2limited, Kohido, a large Japanese car light factory, estimates that by 2008 all new cars will use LEDs as their lights.

2 White LED card light

A domestic optoelectronic device Co., Ltd. is a new white LED product named “card lamp” for Japan Daigong. The actual product is shown in Figure 1. This is a new application of white light LED, which has been patented.
 

Analysis of the structure and working principle of white LED card lights

2. 1 The structure and principle of LED card lights

The LED card lights currently manufactured are mostly small in size, and the area of ​​the light-emitting part ranges from 3.81 cm (1.5 traces ┑ 6.0 cm (2.4 traces). The structure is divided into frame, backlight module, flashing circuit, power supply part, Five parts of switch:

(1) Frame

The frame is used to install and integrate other parts to make it into a whole, which can be processed into different geometric shapes according to different needs. The card lamp in Figure 1 is rectangular.

(2) Backlight module

The backlight module is the most important part of the card light, which determines the light-emitting area and luminous quality of the card light. The backlight module is composed of an LED lamp, a reflector, a light guide plate, a diffuser, a light shield, an antireflection prism, and a backlight frame. LED lights are the light source. The light guide plate spreads the light emitted by several LED lights to the entire light emitting surface. The diffuser plate makes the light emitted more uniform by the principle of diffuse reflection. The antireflection prism can change the angle of the emitted light and gather more light. In the direction of the front viewer, the shading plate is used to control the light-emitting area and the shape of the light-emitting surface.

(3) Flashing circuit

The flashing circuit is usually installed inside the card light, and the light-emitting part of the card light is adjusted to emit several different modes of light by controlling the switch.

The ordinary flashing circuit can provide three modes: constant light, long interval flashing, and fast flashing.

(4) Power supply part

The working voltage of the LED is around 3 V. Due to the power saving feature of the LED, the power supply for the card lamp can be a button battery. The card lamp powered by a button battery has a compact structure and can be made into a product with a smaller thickness. A removable rechargeable lithium battery can also be used. The advantage of using a rechargeable lithium battery is to save resources. If the card lamp is used frequently, it is more reasonable to use a rechargeable lithium battery.

(5) Switch

Used to connect the circuit and the power supply, adjust the card light on, off and light-emitting mode.

2. 2 Brightness test

The brightness of the test card lamp adopts a multi-point luminance meter (BM-7). BM-7 has 4 measurement angles such as 2°/1°/0.2°/0.1°, etc., and the minimum measurement area can reach φ0. . 1 mm. It can measure brightness L, chromaticity X, Y, three color values ​​X, Y, Z, color temperature, response time, contrast, etc. It is widely used in the measurement of LCD, BLU, LCM and other fields, and it is the standard of the LCD industry.

3. 8 cm (1.5 traces ┑ meshes: Puxin Jiaoqi pendant LED, using BM-7, the light-emitting area is 3. 8 cm (1.5 traces ┑ meshes) Shown in Mei Nuo Lai Li Yuan ā 2 馐 Fate Lot Hui Meng Bin 2.

Analysis of the structure and working principle of white LED card lights

Choose 5 LED backlights, choose the test instrument TOPCONBM-7, the test distance is 50 cm, and the test condition is the current I = 20mA. The measured brightness values ​​of 9 points are shown in Table 1 (unit is cd/O):
 

Analysis of the structure and working principle of white LED card lights

2. 3 data analysis

The calculation formula of uniformity R is:

Analysis of the structure and working principle of white LED card lights

Calculated from the above formula, the uniformity of the effective light-emitting parts of the five groups of backlights are 92%, 86%, 93%, 92%, and 88% respectively. The maximum uniformity has reached 93%, and the minimum is 86%. All the uniformity is above 85%, which shows that the light source uniformity of the card lamp and so on is already very high. The last item in the table is the average value of 9 points in each group. The fourth group has a lower value. The analysis may be due to the installation process.

Excluding the fourth group, they all exceed 3 400 cd/m2. Usually, the brightness of more than 200 cd/m2 can meet the application.

In order to visually compare the brightness of each test point, take the average value of five brightness for each point to make a three-dimensional surface diagram as shown in Figure 3. The horizontal axis and vertical axis of the horizontal plane indicate the location of the measurement point, and the number of points is used to label Note, the vertical numerical axis represents the average brightness of 9 points, the unit is cd/m2.

The above data shows that the brightness and uniformity of the card lights are very good.

However, it can be seen from Figure 3 that the edge brightness of the light-emitting surface is high, and the center brightness is low. This point needs to be improved in the future.
  

Analysis of the structure and working principle of white LED card lights

2. Application of 4 card lights

LED card lights have many applications in daily life. White LED card lights are light, thin and environmentally friendly. They are usually integrated into other commodity structures. Translucent cards (such as business cards, labels, holiday cards, etc.) can be attached to the light-emitting part of the card lights. When the card light is on, especially in the dark, the content of the card will be highlighted. In addition to the white card lights, red, green, and yellow LEDs have been used to make colored card lights. The gift box is equipped with this kind of colored card light, which can play a decorative role. In addition, because the card light is equipped with a flashing circuit, the flashing light can attract people’s attention, so the card light is also used for safety.

3 concluding remarks

With the successful development of 100 lm/W white light LEDs, the popularization of white light LEDs in Display and lighting applications has taken a step forward, and there are more and more new devices made of white light LEDs. The European Union has stated that it will completely replace incandescent lamps with LEDs within two years, and the Chinese government has also launched a green lighting project. What is certain is that with the increasing application of white LEDs in automobiles, display backlights, and lighting appliances, the LED era is bound to come soon.

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