In the past two years, small pixel LED displays have been successful in the security field and high-end conference market. In Indoors, especially on the cinema line, small pixel LED displays have an absolute advantage.
1 point to point display advantage
The 4K projector can only achieve high-definition picture quality in the center area of the screen because the distance from the projector to the center of the screen and the four vertices is not the same, and the defocus problem usually exists at the edges. In addition, due to the arrangement of three primary colors, the problem of misconvergence also exists at the edge of the screen, causing the problem of colored borders. Therefore, choosing a good seat is a prerequisite for ensuring the best effect of watching movies.
The LED display adopts the point-to-point control method. The screen can be normally displayed in the center and the edge area. There will not be any missing display information and distortion of the screen. This is a problem that the projector has been unable to solve, but it is the advantage of the LED display.
2 brightness and contrast advantages
As we all know, the brightness of LCD TVs we commonly use is in the range of 131-175 FL (450-600 cd/m2), and even the brightness of home projections exceeds 12 FL (41 cd/m2). Obviously the brightness standard of 16-3+6cd/m2 is too low.
Although the proposed SMPTE proposed moderate brightness standard for full darkness, the recommended value is 12~16fL (Foot Lambert). The brightness value of 2D movies can basically meet the requirements, but the brightness value of 3D stereoscopic movies is obviously insufficient. This is the reason why 3D movies are criticized. The important reason is that the long-term effect of it is causing dizziness and eye pain.
The LED display does not have the problem of insufficient brightness. The LED display factory can ensure that the LED display can achieve different brightness by selecting suitable lamp beads, driving ICs and controllers, and designing a reasonable circuit. In the development of the small pitch in recent years, the brightness is lower than 500cd/m2, the refresh rate exceeds 3840Hz, and the appearance of the grayscale 16bit technology has laid a technical foundation for the small pitch in the indoor area.
3 luminous advantages
Movie playback is a process of passive lighting. It shines light on the screen and reflects it in the human eye. During this process, the positional relationship between the two projectors causes light and light to interfere with each other, causing some The picture is blurred, especially in a dark environment.
For this reason, the screen is usually a non-smooth surface. Designers use the diffuse reflection principle to reduce specular reflection, but the reflection phenomenon still exists. The LED display is active and the diffuser design is used on the surface mask to fundamentally eliminate the interference between light and light. This is impossible for the projector to do!
The LED display has no place for the projector to match, but there are still problems to be solved when it comes to really entering the cinema line:
1 meet the movie standards
LED display factory, encapsulation factory, chip factory and drive chip manufacturers should work together to help led display screen pass through the DCI-P3 certification, at present mainly from the light-emitting devices and light-emitting device application technology. The major wavelengths of light emitting tubes shipped in the industry are: red 620-630 nm; green 520-530 nm; blue 465-475 nm. According to the color coordinates specified in the foreign document DCI-P3 (Figure 2), the conversion wavelength values are as follows: red 615 nm, green 544 nm, and blue 465 nm.
Looking at the LED chip data and measured data, we found that when the driving current is<5mA, the dominant green and blue wavelengths are greatly affected by the current. The use of small pixel display current is just below 5mA, green and blue is usually about 2mA, and the cinema line due to low brightness requirements, the actual use of the current will be less than 3mA, or even less than 1mA, so on the one hand, need to be in the chip factory By adjusting the wavelength range of the chip, the packaging plant reduces the current actually used by the display of the theater line by reducing the separation and separation current. It is learned from the upstream chip that if non-primary BIN chips are needed, there are two major problems: output and cost. Adjusting the band based on the out-of-band adjustment will result in more partial-wave output loss and distribution of output. , to be further proof of chip manufacturers. Similarly, after adopting the new current standard separation and color separation, the packaging plant has similar problems with the chip factory, and these output and cost problems are solved depending on market demand.
On the other hand, the LED display factory needs to cooperate with the chip factory to design a reasonable circuit and select or develop a driver chip with a higher current output accuracy.
From a technical point of view, it is feasible to produce a display that meets the DCI-P3 standard using a polarized wavelength. Through the efforts of all parties in the entire supply chain, LED display can enter the cinema market with more perfect picture quality.
2, meet the stereo effect
The requirement of the display for the sound is to be able to synchronize with the video, and the playback and processing of the theater audio is considered to be as important as the screen display.
According to reports, the world’s first DCI-P3 LED display, launched in Las Vegas, surrounds the screen with speakers. To ensure sound quality, the display factory uses proprietary audio processing technology and JBL’s Sculpted Surround system. .
It is understood that the theater stereo implementation consists of main channel speakers, subwoofers and surround speakers. In addition to the surround sound speakers distributed on the side walls and back walls of the auditorium, the main channel speakers and subwoofers are mounted behind the screen. Among them, the main channel speaker is composed of left, middle and right channels. Since dialogue characters are generally located in the middle of the screen, the stereo must be increased in order to avoid backward movement and reduction of the best listening position or separation of sound image and image. In the middle information, the speaker is placed behind the screen, and the sound to the audience feels like it is natural;
Given the current stereo sound system in cinemas, large-size displays cannot be realized temporarily with display screens with speakers arranged at the edges of the screen. The LED display released in Las Vegas is about 10.3 meters long and 5.4 meters high, which can meet the needs of the screening of the basic theater, but when the screen is currently the mainstream IMAX (standard IMAX screen is 22 meters wide, 16 meters high), even larger, how can such a LED display to achieve the perfect combination of audio and video, to be demonstrated.
The author thinks that the LED display screen is superior to the display effect, but whether it can achieve a certain sound penetration rate like the screen on the realization of stereo effects will be a key step for the LED display screen to win the market of the movie theater line.
3 The proportion of bright and dark areas
The fill factor is also called the bright area ratio, which is the ratio of the light emitting area of each pixel to the physical surface area occupied by the pixel. There is a non-light emitting area between the pixels of the LED display, and when viewed at a close distance, a noticeable graininess appears. Therefore, we propose a minimum viewing distance. According to the TCO’99 standard, the fill factor should not be lower than 50%. The following table shows the fill factor of the LED display:
It can be seen that in the selection of the lamp beads, we choose the lamp beads that are close to the dot spacing size as much as possible, which can increase the filling factor and reduce the graininess of the screen.
4, reliability issues
The reliability of the projector is determined only by the projector itself, and the LED display is composed of a plurality of components, and the reliability of its component parts directly affects the reliability of the entire display.
Failure rate of LED display=nλp=∑ni*λi*Wi
Λp—The failure rate of the module
Λi - Failure rate of component i
Ni - the number of parts
Wi - the importance factor of the part
For viewers, the most tolerant of watching LED displays is: black screens or the presence of no signal areas, most of the time due to the failure of the switching power supply. For example, the reliability of a certain power supply MTBF within the industry is 150,000 hours. Assuming that the movie is played for 12 hours/day, the annual failure rate of this power supply is 0.0292 from λ=12*365/MTBF=0.0292, which is calculated on the basis of 12 hours per day. Assuming a 352-m2 giant-screen movie, the production of a P2.5 display requires about 422 sets of power. The annual failure rate of the full-screen power supply is 12.3224. If dual-supply hot backup technology is used, the probability of simultaneous failure of the paired two power supplies is negligible. of. Therefore, the problem of power failure can be basically solved.
Compared to projectors, the failure rate of LED displays is higher than that of projectors because of the hugeness of the system. Therefore, if you want to truly push the LED display to the cinema market, the improvement of reliability is an important system project in the industry.
5, the cost problem
The high cost is currently a major obstacle for LED displays to enter the cinema market. Cost components are divided into material costs and operating costs. Examples are as follows:
Assumed shadow room: 350 m2, 170 seats (small projection hall), screen 17*9(m)
According to Sweden's TCO’99 standard, line-of-sight S≥1718*point spacing. Therefore, by calculation, the distance between points that meet the 17m-wide display screen is at least 4.94mm, which is calculated by taking 4mm.
In addition, the same area of LED display and projector power consumption difference of more than 4 times. However, with the continuous decline in the cost of LED devices, coupled with the continuous development of energy-saving technologies, the cost issue will gradually weaken.
6, security considerations
LED display security can be considered from two aspects, one is personal safety; the second is personal health.
a. Personal safety
There is a certain risk of burning in the LED display's own heat. The LED display is mainly composed of modules. The module housing is usually made of metal. The possible burning parts are: LEDs, PCBs, switching power supplies, wire rods, and plastic parts. Therefore, the selection of flame-retardant or non-combustible materials is the basic requirement for LED display screens to enter the cinema line. In addition, the LED display itself has a temperature, smoke monitoring and alarm system. It is feasible and inevitable that the system accesses the overall monitoring and alarm system of the cinema after the display enters the cinema line.
b. Personal health
The minimum line of sight of the theater is at least equal to or greater than half the width of the screen, and the width of the theater's screen is usually not less than 8m. Assume that the minimum line-of-sight is 4m, which is closer to the audience, according to the width of 8m. Therefore, we must consider the effects of thermal radiation and electromagnetic radiation on the human body.
In order to protect the viewer's health and safety, in different occasions, LED display screens entering the cinema line need to pass different certification standards, such as CCC, ETL, CE, FCC, RoSH and so on.
LED displays have advantages such as point-to-point display, high brightness and contrast ratio, and active light projectors. From a technical point of view, it is feasible for LED display screens to enter the market of movie theaters, but it is also necessary to meet the standards of movies and provide acoustic display. Improve the proportion of bright areas, reliability, security and other aspects of the upgrade, the current situation, the LED display screen costs need to further decline in order to have the opportunity to compete with the level of laser projection, and reliability will be LED display station An important indicator of steady development and sustainable development.
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