LCD 백라이트를 위한 LED 드라이브 시스템의 고성능 제어

Thermal effects were investigated in a liquid crystal display (LCD) backlight unit (BLU) that was composed of light emitting diode (LED) arrays. The driving power for a single LED in a BLU is determined by the desired brightness of the LCD panel and the pitch distance between adjacent LEDs. As the pitch distance increases, individual LEDs need to be driven by a higher power in order to maintain the same brightness. Since the junction temperature of an LED plays an important role in LED performance, such as optical efficiency, intensity degradation, and lifetime, the maximum driving power for an LED should be limited by a critical level of the junction temperature. A guideline for designing LED BLU panels taking account of the junction temperature is presented using various parameters of LED arrays.

This work presents a multiphase multilamp driving system for liquid crystal display (LCD) back light The driving system adopts a multiphase inverter to drive cold cathode fluorescent lamps (CCFL) to reduce input current ripple. Furthermore, to prevent current imbalance among lamps a multiphase transformer is introduced in the proposed system. Compared with the conventional single-phase driving system, the proposed one can have the merit of requiring less number of transformers. A three-phase driving system with current balancing transformer has been built, from which experimental results have verified the feasibility of the proposed multiphases driving system.

The International Telecommunication Union Radiocommunication Sector (ITU-R) Recommendation BT.2020 was standardized for ultra-high definition television (UHDTV). The BT.2020 specifications are 8K resolutions, a wide color gamut, and 120-Hz driving. The BT.2020 color gamut is defined from the three primary monochrome colors. Therefore, changing the light source of the backlight from conventional light-emitting diodes (LEDs) to lasers is necessary. We succeeded in prototyping a 17-inch 8K liquid crystal display (LCD) that satisfies the BT.2020 specifications. The pixel density of the 17-inch 8K display is 510 ppi, and the color gamut covers 97% of BT.2020. The liquid crystal response time is 5 ms, which is sufficient for the 120-Hz driving. To achieve the above-mentioned specifications, we developed the following technologies. To expand the color gamut, an RGB laser backlight was used. A backlight with conventional LEDs as light sources only covered 52% of BT.2020. To reduce response time, we applied a faster in-plane switching LCD (IPS-LCD) named short-range lurch control (SLC) IPS-LCD. We succeeded in realizing a blur-free display using the SLC IPS.

We developed two mobile-device size autostereoscopic integral videography (IV) displays with field sequential color (FSC) liquid crystal displays (LCDs) and micro lens arrays. IV is an autostereoscopic video technique based on integral photography. The FSC-LCD has a different backlight from that of conventional LCDs. The backlight is produced by red, blue, and green light emitting diodes (LED) instead of by cold cathode fluorescent lamps, and each LED emits light sequentially. IV based on FSC-LCD doesn't cause color moires because the FSC-LCD does not require color filters. One FSC-LCD IV display is 5-inch diagonal with 256×192 lenses and 20 ray directions. Its base FSC-LCD is 300ppi with 1280×768 pixels. The other FSC-LCD IV display is 4.5-inch diagonal with 192×150 lenses and 80 ray directions. Its base FSC-LCD is 498ppi with 1920×1200 pixels. In this paper, we first describe the problems of a previous conventional LCD-based IV displays, and then describe the principle of the IV displays based on the FSC-LCDs. Next, we analyze the IV displays by a plenoptic sampling theory. Lastly, we compare three versions of the IV displays, two based on the FSC-LCDs and one based on the conventional LCD.

Color gamut and static and dynamic color shifts of a multi-domain in-plane-switching liquid crystal display (IPS LCD) are calculated quantitatively using RGB (red, green, and blue) light-emitting diodes (LEDs) and cold-cathode fluorescent lamp (CCFL) backlights. Simulation results indicate that the LED backlight exhibits a wider color gamut, better angular color uniformity, and 2-4X smaller static and dynamic color shifts than the CCFL system.

In this study, we would like to tune the color temperature of the high power phosphor Light-Emitting Diodes (LEDs) with the single LED of red, green, yellow and blue, respectively. The starting color temperature of the white phosphor LED will be set at 7500K (D75 white light), then changing the voltage of the single LED of the red, green, yellow and blue, respectively, to find the best tuning function for the color temperature and luminous efficiency. These results exhibited that changing the voltage of red LED had the broader color temperature from 7500 K to 1500 K and low luminous variation from 54 to 41 lm /W than green and blue LEDs. Though the green and yellow LEDs had the low luminous variation from 47 to 51 lm /W and from 40 to 47 lm /W, respectively, but the color temperature of green and yellow LEDs could only fine turn from 7500K to 8200K and 4700K to 7500K, respectively. The luminous efficiency had rapid variation from 27 to 42 lm /W and out of the color temperature of 20000K for the voltage tuning of blue LED. Therefore, the voltage tuning of red LED could show the warm color temperature for the human life. The variation of color shifts (Δuv) of red and green LEDs changed from small to large with the increasing of the enhanced voltage. But the variation of Δuv of the yellow and blue LED changed nothing with the increasing of the enhanced voltage.

Dual-panel liquid crystal displays with wide colour gamut and high luminance

Light emitting diode (LED) is widely used in lighting field. LEDs are revolutionizing the automotive lighting industry, as they are often much more durable, efficient and energy-saving than various traditional car headlight technologies. Blue light emitted from GaN LEDs can be used to stimulate a wider spectrum of emission from the phosphor layer around the LED to create white light. Although LEDs are more efficient than previous lighting technologies, there are still some scientific and engineering challenges need to be overcame, such as with the drive current increases, the efficiency of LEDs is significant decreases. This phenomenon is known as LED droop. Therefore, in order to increase the brightness, it is necessary to use more LED chips, rather than simply increase the drive current. The cost of LED products will increase. At present, the suppression of LED droop is one of the important ways to reduce the cost of LED products. In this work, we focus on suppressing the LED droop and improving the luminous efficiency of LED. To solve above problems, a flip-chip GaN P-N junction model is investigated. The configuration is composed of a three-layer structure. Besides, the P-N junction is analyzed and optimized. The characteristics of proposed LED configuration are investigated by using finite element method (FEM). Research results show that internal quantum efficiency (IQE) drops drastically when current density exceeds 180 A/cm^2, and the luminous efficiency of the device is high when the current density is 100-180 A/cm^2.

Luminescent thermal stability and electronic structure of narrow-band green-emitting Sr-Sialon:Eu2+ phosphors for LED/LCD backlights

II. Evaluation of the impact of alternative light technology on male broiler chicken stress

Quantum dots (QDs) are one kind of photoluminescent materials with excellent properties, such as adjustable spectrum, narrow full width at half maximum (FWHM), and high color gamut. In this paper, a photoluminescent QDs printing paste suitable for light guide dots array applied in the backlight for liquid crystal display (LCD) was presented. The QDs printing paste was first prepared and characterized with different kinds of solvents. Then, triphenyl phosphite (TPP), a kind of antioxygen, was added into the QDs printing paste to improve the stability of the QDs printing paste. Finally, a QDs light guide plate (LGP) was fabricated by screen printing with QDs printing paste added with silicon dioxide (SiO2) light scattering particles. The color gamut of QDs LGP arrived 131.6%NTSC due to light scattering interaction between blue LED, red QDs, green QDs, and SiO2 particles. The results showed that the QDs‐chloroform printing paste had uniform light output and the highest photoluminescent peak intensity. Therefore, the composite screen printing paste has wide application prospects in the backlight of LCD, with the advantages of simple process, high production efficiency, and low cost.

Thermal characteristics of light emitting diode (LED) devices directly effects on the luminous efficiency and long term reliability of LEDs. Junction temperature and thermal resistance are the main parameter that reflection of the heat dissipation capability of the LED device. In this study, relationships between thermal resistance and luminous flux and electrical power are simplified based on the photo-electrothermal theory. A new method using the optical-electrical characteristic of the LED is proposed to measure thermal resistance and junction temperature. The calculation of thermal resistance of the LED utilizes the reduction rate of luminous efficacy with the increasing temperature k e , heat dissipation coefficient k h , heat sink temperature T hs and the electric power corresponding to maximum luminous flux P d ∗. The thermal resistances of different brands and different power of LED devices are measured; the measuring results are highly consistent with nominal thermal resistance, which confirms the feasibility and generality of the proposed method. This method is simple and credible, and requires no expensive thermal measuring instruments, making it valuable for engineering application.

An InGaN/GaN blue light emitting diode (LED) structure and an InGaN/GaN green LED structure were grown sequentially onto the same sapphire substrate so as to achieve a nitride-based near-white LED. In order to avoid the thyristor effect, we choose a large 1 × 1 mm2 LED chip size, which was six times larger than that of the normal LED. It was found that we could observe a near-white light emission with CIE color coordinates x = 0.2 and y = 0.3, when the injection current was lower than 200 mA. It was also found that the output power, luminous efficiency and color temperature of such a near-white LED were 4.2 mW, 0.8l m/W, and 9000 K, respectively.

Increased use of cars that are not balanced with the provision of adequate parking areas and many drivers who park in any place. The existing parking system only utilizes the parking area and the parking attendant who controls it. Motorists also have to find a place that is free of parking officers or drivers do not pay attention to the parking area, the vehicle owner will look for must get out if you do not get a parking space. To overcome this, make a parking system by using a microcontroller system that facilitates vehicle users to understand the number and arrange an empty parking space. The design of this parking system discusses the available parking system which will be notified via LCD (Liquid Crystal Display) and LED (Light Emitting Diode) at the entrance of the parking lot, and also so that it can be used for the total vehicles in the parking lot with LED indicators ( Light Emitting Diode). This design uses the Arduino Nano as a processor to process data. The servo that translates the bar will be driven. When the parking lot is full, the LCD (Liquid Crystal Display) gives information that there is no vacant land, so the parking user goes up to the next floor. From the Arduino test results, Nano can adjust the circuit well, and Ultrasonic sensors can connect vehicles in each parking area, and the servo bars can be opened and closed again.

Evaluation of exposure time and visible light irradiation in LCD 3D printing of ibuprofen extended release tablets