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Cadillac's first EV to exhibit "Lyric" ... Shanghai Motor Show 2021
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In addition, special details such as a backlit speaker grill and a curved screen with hidden storage have been introduced.
Cadillac will showcase the brand's first EV "Lyric" (Cadillac LYRIQ) on April 4th ... → Continue reading
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There are two types of backlight: edge light method (both side light method and light guide plate method) and direct type, but small liquid crystal and notebook type.computerandLCD monitor, Many popular LCD TVs have an edge light system, which is larger than that of intermediate-sized TVs with large screens.liquid crystal televisionThe direct type method is mainly adopted for.Utilizing the light guide plate, which is the key to edge light technologySurface light sourceTechnology isJapanIt originated.
At the beginning of the dawn of liquid crystal displays, the backlight meant the edge light method, but in recent years, the direct type has become the mainstream for backlights for LCD TVs, so the edge light method and the direct type method may be described separately. preferable.
IncidentallyOrganic electroluminescenceThe (organic EL) display itself is a light emitter, so it is not equipped with a backlight.
Use as a light source for large-area objects such as LCD TVs and PC displaysCold cathode tubeCurrently, there are few examples of using, and liquid crystal displays have a wide color reproduction range of RGB 3 colors.LEDMost of them use as a light source.In addition, LEDs are suitable for miniaturization because they do not require a high-voltage power supply, and most battery-powered portable electronic devices use white LEDs or three-color LEDs.
There are the following types of light sources:
- light bulb
- Light emitting diode (LEDs)
- ElectroluminescencePanel (ELP)
- One or moreCold cathode tube (CCFL)
- Fluorescent light(HCFL)
When displaying colors with LEDs, light sources of the three primary colors of blue, green, and red light are required. In the case of a monochromatic light source such as an LED, a pseudo-white LED that excites a yellow phosphor to be a white light source by a single-wavelength blue LED may be used, but in this case, the display is limited to a single color.In some cases, a pseudo-white LED is used as a light source and further separated into two colors by a filter, but there are few practical examples. In the full-color system using monochromatic light of each RGB as the light source, the color reproduction range is wider than that of the cold cathode fluorescent lamp.
Edge light method
The founder of the edge light method, which is the mainstream in small LCDs, is1985Founded in Shiga Prefecture, the inventor is Shinzo Murase.
The LCD backlight is an unsung hero behind the LCD industry, and along with the LCD technology that originated in Japan and is being worked on by giant companies, it is another original that was invented and grown by the hands of Japanese SMEs. It is a technology.Initially, this surface light source technology was developed for signboards, but Matsushita Electric was the first notebook type to appear at that time.word processorIt became popular because it was adopted in.After that, ToshibaDynaBookThe edge light method was recognized as the mainstream of LCD backlights.For LCD backlights at that timeElectroluminescenceWas used, it was dark and had a short life.ItCold cathode tubeThe life was extended by adopting the above, and the brightness could be improved by combining the cold cathode tube and the light guide plate.And, with the invention of the light guide plate, it is indispensable for the light guide plate.Cold cathode tubeEven the industry of.Traditionally, Japanese manufacturers have taken the lead in the global cold-cathode tube market, but in recent years Taiwan, South Korea, and China have emerged.Gradually as a light source for thin displays, mainly for portable electronic devicesLEDThe ratio of is increasing.
The operating principle of the edge light type backlight is shown below.
For the light sourceCold cathode tube(Cold-Cathode Fluorescent Lamp, CCFL) is used.Light emitting diode(LED) has been used for small LCDs for mobile phones, etc., but is also being adopted for large LCDs for desktop PCs...The edge light type backlight is a combination of these light emitting sources with a reflector and a light guide plate.The light guide plateア ク リ ルWhite on the boardイ ン クSilk printing method that printed reflective dots withinjectionThere are a molding method in which the acrylic surface is made uneven, an adhesive dot method in which an acrylic plate and a reflector are attached with a dot-shaped adhesive material, and a method by grooving.Grooving methods include a grooving method for mechanically carving and a non-contact laser processing method.
Light emitted from a light source such as a cold-cathode tube or an LED is incident from the side of the light guide plate, and at this time, almost all light except for surface-reflected light (approximately 7%) is incident on the light guide plate.The light incident on the light guide plate repeats surface reflection and spreads over a wide area of the light guide plate.If there are reflective dots at this time, the light is scattered there, and the light goes out from the surface of the light guide plate.The light guide plate is devised so that the entire light guide plate shines uniformly by reducing the area of the reflection dots near the light source and increasing the area of the reflection dots as the distance from the light source increases.
The light guided from the light source into the acrylic light guide plate is guided to the entire surface of the acrylic using the total reflection of acrylic, and the light that hits the reflection dots changes its course, and the light that is smaller than the total reflection angle is generated. The entire surface of the light guide plate is made to shine uniformly by utilizing the fact that it comes out from the acrylic surface.With the non-contact laser machining method, machining can be performed from one sheet at a time, and each time, the groove distribution can be designed in consideration of the size of the surface light source, aspect ratio, and light entering side to achieve surface balancing. It is possible.Laser processing is a step in the finish, but when the quantity is large, the mainstream is to make a mold and perform injection molding.The adhesive dot method is advantageous for ultra-large backlights.In some cases, the design of such reflection dot distribution and groove distribution is designed using computer simulation technology.
In small devices such as mobile devices and automobile devices, the light source is often placed on only one side with respect to the left, right, or top and bottom of the panel, but for PC monitors, amusement machines, and medium / small screen sizes. LCD TVs are often placed at both ends, and large-screen LCD TVs and digital signage may have light sources placed on all sides.
Compared to the direct type method, the edge light method has the advantages of being easier to make thinner and lighter, having better power efficiency because it uses a light source with a large luminous flux and arranging fewer light source elements, and it is easier to dissipate heat. It is widely used in LCD panels for mobile devices, automobile devices, amusement game machines, etc., as well as general monitors and popular LCD TVs.However, it is difficult to irradiate the entire area uniformly and stably compared to the direct type method, and it is difficult to partially control the fine-grained backlight (even with this method, LCD TVs that realize partial control close to the direct type). (Although there is), because the light is emitted from one side and the screen is illuminated by the light guide plate, color unevenness, illuminance unevenness, moire, etc. are likely to occur due to partial characteristic differences of the light guide plate and reflector, slight distortion, etc. There are drawbacks.
Direct type method
As the name suggests, the direct type method is a method in which light sources are evenly arranged directly under the liquid crystal panel, and the light emitted is diffused onto the panel via a diffuser plate to directly illuminate the screen. This method is used for high-end machines with relatively large screens.Compared to the edge light method, stable irradiation with high uniformity is possible, and it has the advantage of being less likely to cause uneven illuminance and color and being excellent in color development and gradation expression, and is suitable for large screens.In addition, the partial control of the backlight makes it easy to finely control the technology (backlight area control, local dimmering) that enhances the expressiveness of black by partially suppressing the illuminance in the shadow area. Widely used in medium- and high-end TVs.However, it is difficult to make it thinner due to its structure, and since many light emitting elements are required when using LEDs, it has drawbacks such as slightly inferior power efficiency compared to the edge light method and slightly difficult heat dissipation measures, so it is a general monitor. It is not often used in mobile devices and mobile devices, and in some models that require thinning, edge light type LEDs are used in LCD TVs even for fairly large screens and high-end models.In addition, there are manufacturers that adopt the direct type method for popular LCD TVs with relatively large screens, but in many cases the number of light emitting elements is reduced due to cost compared to high-end models, so in the four corners It is important to note that some products are prone to eclipse (a phenomenon in which the four corners of the screen are shaded and darkened).