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>> The Influence of LED Backlight on LCD Color 7th,MAY,2018
With the rapid development of society today, competition in many industries has become increasingly fierce. The TV market is no exception. The television industry has experienced CRT TVs, plasma TVs and LCD TVs for 10 years. Today, CRT TVs and plasma TVs have basically disappeared, and the market share of LCD TVs has reached over 99%.
In a liquid crystal television, the liquid crystal display itself does not emit light because it is a passive display device, but it can still display a graphic image through the backlight through the liquid crystal display panel. The performance of the backlight will affect its various major indicators. Therefore, the performance of the backlight of the LCD TV largely determines the display effect of the LCD TV, such as brightness, color, etc. Therefore, both at home and abroad, Liquid crystal display researchers are working hard to develop excellent backlight products. There are mainly two kinds of backlights for LCD TVs: one is CCFL (cold cathode fluorescent lamp, which is our common fluorescent lamp); the other is LED (light emitting diode). At present, LED backlight has basically replaced CCFL backlight to fully occupy the market. Compared with CCFL backlight, LED backlight has many advantages, mainly reflected in the following four aspects:
First, LED has a wider color gamut. The CCFL emits light by exciting phosphors. The spectrum of light in different wavelengths has more components, resulting in a low color gamut. The NTSC color gamut is usually only about 70% at the highest. The LED's emission spectrum is very narrow. By choosing the right LED, the NTSC color gamut can reach more than 100%, and the color gamut of the CCFL backlight is extended by about 50%.
Second, LED life is longer. In general, the service life of CCFL is between 8000 and 100,000 hours, and the lifetime of LED can reach twice or even longer than that of CCFL.
Third, LED environmental protection and energy saving. One of the main elements indispensable to CCLF backlights is mercury, mercury, which is harmful to humans. For LED backlights, it is completely mercury-free and meets the requirements of green environmental protection. And the LED backlight source is very power-efficient, and the power consumption of the LED is lower than that of the CCFL. Fourth, the LED is smaller. For LCD TVs to be made ultra-thin, there are mainly two decisive factors, namely, the thickness of the backlight module and the power supply substrate, among which the backlight module is the largest deciding factor. The size of the CCFL backlight is basically fixed and there is basically no reduction in margin. Smaller LEDs can make the backlight module smaller, such as the 40-inch Samsung side-entry LED TVs, whose backlight module is only about 5mm thick.
Most of the LED backlights use white LEDs, which use blue LED chips to excite the fluorescent material to emit white light. Because there are differences between the materials used by different manufacturers and the manufacturing processes of the LEDs, the LED spectrum and brightness of different manufacturers also have a certain degree of difference. Therefore, when modulating the liquid crystal screen, it is necessary to understand the characteristics of the light response of the LCD screen to the LED backlight. In this experiment, under the LED side backlight source structure, the effects of driving current on LCD brightness, LCD color coordinates, brightness of LCD three primary colors (red, green and blue), and the color gamut of LCD were studied.
1 test structure
The LED-side backlight structure includes a white LED, a light guide plate, a 1-layer reflector, a 1-layer diffuser, a 2-layer diffuser, and a liquid crystal panel. A white LED is placed on the side of the light guide plate, and the white LED emits light. After the light enters the light guide plate, the light guide plate is used to transmit the light. The light guide plate can evenly distribute the light, and the reflection plate can reflect light to make the light go to the liquid crystal screen. The direction of propagation, and then the light through the diffusion film, the first layer of light enhancement film and the second layer of light enhancement film, to the liquid crystal screen to make the LCD screen light.
2 test and test system
The luminance meter SR-3A is the instrument that we mainly use in the test, there are Chroma29135 liquid crystal module automatic test systems, oscilloscopes, current probes and so on.
2.1 Test System Composition
The luminance meter SR-3A measures the brightness and coordinate value of the LCD screen; the Chroma29135 LCD module automatic test system mainly transmits the electric signal to the LCD screen, which drives the LCD screen, so that the LCD screen displays the image; the oscilloscope and the current The probe is responsible for recording the value of the LED backlight driving current when the LCD TV is lit. In order to avoid external light affecting the test system, the entire experiment was conducted in a dark room.
2.2 Test Conditions
The aperture angle of the luminance meter is set to 2° and the same is guaranteed. The measurement distance L is set to 500 mm, the temperature is maintained within the range of 25°C±3°C, the humidity is maintained within the range of 60%±20%, and the last five groups are selected differently. The current data is tested.
2.3 Measurement position
The 13 measurement positions are evenly selected on the LCD screen, as shown in Figure 1.
The Influence of LED Backlight on LCD Color
Figure 1 Measurement 13 specific test positions of the LCD screen
2.4 Test Content
The first test is a white screen, then the three primary colors (red, green and blue) are tested, and finally the tests are performed in different current conditions.
2.5 Test Methods
First, record the surrounding environmental conditions, then prepare the LED backlight system and place it in the center of a test platform. The LED backlight system is turned on. After the 20-minute backlight system is stable, the first measurement point is located and the center point of the luminance meter is aligned with this measurement. Then 13 predetermined measurement positions are measured in turn, and the luminance and The color coordinate data is recorded, and the measurement of the white screen is ended. The three primary colors are replaced and the previous steps are repeated, and measurement is performed in turn.
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