#3lcdprojector

As known, a multimedia projector provides image projection on a large screen. Of course, it requires an external video content source, such as a computer, DVD player, TV tuner, WiFi, etc. Today, media projectors are among the most popular devices. Of course, companies respond adequately to high demand, offering a huge range of different models. This list includes 1-chip (DLP) and 3-chip projectors based on DLP, 3LCD or LCoS (D-ILA, SXRD) technologies using mercury UHP or xenon lamps, or semiconductor (laser, LED or hybrid) light sources. Of course, such a variety is accompanied by a huge difference in the basic technical spec and functionality of the models. Therefore, even their simplified classification can simplify the selection of the optimal model. This list includes: - the matrix resolution and its physical format (4: 3, 16: 9, 16:10, etc.); - projection image technology; - brightness of the light flux; - 3D support; - interfaces; - contrast ratio; - lens characteristics; - light source; - functionality; - noise level (20-24 dB); - parameters of the projected image (throw ratio, image size, etc).

Resolution and format

The resolution of the matrix depends on the number of pixels of liquid crystals or micromirrors. Modern models support the following formats: 4: 3 aspect ratio: -VGA (640x480); -SVGA (800x600); -XGA (1024x780); -SXGA (1280x1024); -SXGA+ (1400x1050); -UXGA (1600x1200); -QXGA (2048x1536). Picture format 16: 9, 16:10, 15: 9: -W XGA (1280x768 or 1280x780); -HD720 (1280x720); -W VGA (864x480); -W SVGA (1024x576); -Full HD (1920x1080); -WUXGA (1920x1200); -HD 4K (4096x2400). The 4: 3 format is the main class of installation models and projectors for mobile presentations, and widescreen models lead the class at home and professional cinema. However, the triumphant spread of high-definition standards, widescreen laptops, and Windows Vista has provoked in recent years a trend towards the dominance of widescreen matrices. Most projectors support the most common color systems, including PAL, SECAM, NTSC 3.58 and NTSC4.43. Newer models usually support HDTV format. Of course, perfect playback requires matching the formats of content source and projector. The projector spec contains this value, which corresponds to the real number of pixels. But, as a rule, projectors can receive a signal of another resolution due to the use of information compression. Unfortunately, it distorts the image. The distortion degree depends on the quality of the processing algorithms. In addition, almost all modern projectors support image format setting. Unfortunately, any reformatting reduces the used area of the matrix and, accordingly, the number of pixels.

Projection image technology

The liquid crystals in the 3LCD technology use the light pass, DLP and LCoS (D-ILA, SXRD) technologies use micromirrors and liquid crystals to reflect light fluxes. But today all these technologies successfully compete, having their own advantages and disadvantages.

Brightness of the light flux

The luminous flux of multimedia projectors is measured in ANSI Lm, which was proposed by the American Institute of National Standards (ANSI) in 1982. This unit of measurement characterizes the average value of the projector's luminous flux in nine zones, which are evenly distributed over the screen area of a certain size. The brightness of modern heavy-duty installation projectors can reach 60,000 ANSI Lm. For example, the Christie 4K D4KLH60 provides from 5,000 to 60,000 lm using 3-chip DLP technology and 1 to 12 laser modules as the light source. On the other hand, the brightness of many popular portable (Cube, Pocket, Pico, Mini) projectors does not exceed hundreds or even tens of ANSI Lm. For example, HDMI Pocket M60 projector provides only 85 Lm. As a rule, viewing video content with home theater projectors is usually accompanied by a darkening the room. In this case, even a relatively small brightness in the range from 300 to 500 ANSI Lm provides good contrast ratio. But viewing in a lighted room or in the daytime without darkening requires a higher brightness. A rough estimate of the required luminous flux power can use the empirical formula lm = screen area x light ratio. Usually, it varies between 500-800 for non-darkened rooms and 200-350 - in the case of darkening. But it should be noted that the real luminous flux of the projector, as a rule, does not exceed 80-90% of that specified in the spec. Unfortunately, direct sunlight on the screen dramatically reduces the image quality of even a very powerful projector.

Contrast ratio

As known, the contrast ratio is the ratio of the maximum brightness to the minimum when projecting the white and black fields, respectively. Unfortunately, the lack of a unified measurement standard complicates its use. Some companies calculate the contrast only in the image center. The ANSI method provides for the averaging of measurement data across distributed zones, except the central one, separately for white and black fields. As a rule, this value rarely exceeds 400: 1. Dynamic contrast is measured for a white screen with an open aperture, and then for a black screen with a closed aperture. Of course, dynamic contrast is radically different from traditional ANSI contrast. Almost all leading companies are developing their own technologies to increase dynamic contrast. This technology uses an automatic aperture, which partially blocks the light flux in dark scenes, but totally passes it in bright scenes. Of course, it greatly enhances the image contrast. For example, many modern models provide 50,000: 1 and higher. Today JVC projectors provide maximum native contrast.

Throw ratio

Usually, modern multimedia projectors use zoom lenses with variable focal length. Moreover, many models provide AutoZoom or focus with the remote control. Of course, throw ratio is one of the main spec of the projector. It's equal to the ratio of the projection distance to the width of the image. Standard models have a Pro range of 1.8-2.2, a long throw lens provides 4–8, a short throw lens supports 0.8–1.2. Today, companies offer ultra-short focal laser projectors. They can create images of 80-100 inches diagonally at a projection distance up to 15 inches. Primarily,the choice of screen size depends on 2 conditions: - the distance from the farthest viewpoint should not exceed 5-6 times the width of the screen; - the distance from the nearest viewpoint must be greater than 1.5 screen width.

Projector Light Sources

As known, the light source is one of the main and expensive elements of the projector and significantly affects its choice. Its cost can reach 20-30% of the model value. The power of the light source directly affects the projector brightness. In turn, the brightness affects the requirements for dimming. For example, a low-power portable projector with a brightness of up to 100 ANSI Lm can provide acceptable quality only in a dark room. A powerful 3LCD projectors with a brightness of 2500-4000 ANSI Lm work fine even in diffused light without additional dimming. Unfortunately, even such models do not provide acceptable quality in direct sunlight. But, a powerful lamp requires effective cooling. Therefore, such projectors usually have a fairly high noise level due to a powerful fan. Modern projectors use mercury or xenon lamps, semiconductor (LEDs and laser LEDs) or hybrid light sources.

Lamps

Most projectors traditionally use UHP (Ultra High Efficiency) mercury lamps as a light source.

They combine a relatively low price, ease of replacement and high brightness. The approximate life of modern lamps reaches 3000 - 5000 hours in maximum power mode, and their power varies from 200 W and more. The lamp generates a stream of white. Special color filters in 3LCD projectors or in the color wheel of DLP models divide it into red, green, blue, etc streams. Unfortunately, UHP lamps provide white with a green tinge. Usually, companies compensate for the excess green with optical filter or by limiting its brightness. For example, many models use Dynamic or Cinema image modes. The first mode uses maximum brightness, but with a green tint, and the second mode provides more accurate color rendering, but with reduced brightness. High operating temperature is a major cons of UHP lamps. It requires intensive cooling with a sufficiently powerful fan. Unfortunately, they have a fairly high noise level, which reduces viewing comfort. Therefore, this value is one of the main projector specifications. Setting the optimum lamp brightness mode has a slight delay. Reducing the brightness of the lamp over time also applies to their disadvantages. However, today these lamps are a proven, high-quality, bright and inexpensive projector light source. Powerful xenon lamps generate a more balanced white with a perfectly even emission spectrum, providing more accurate color rendering.

Unfortunately, they are much more expensive and less effective. However, high-end projectors often use them.

Semiconductor light sources (LED and laser LED)

Modern models are increasingly using semiconductor light sources, including LEDs or laser LEDs. They generate a very narrow emission spectrum with pure rich colors that do not require special filters to separate colors from the white spectrum. Of course, this feature is very important for modern video standards, for example, for Ultra HD. Power and cost are the main differences between laser and LED light sources. Laser LEDs, especially green ones, have a higher cost of production, but they provide much more power.

The brightness of the LED light source usually does not exceed 500-700 ANSI Lm.

As a rule, expensive projectors use laser light sources. Portable models based on one-matrix DLP technology often use an LED light source. The segment of portable (Cube, Pocket, Pico, Mini) projectors today leads in the growth of popularity. These models do not have a color wheel and provide instant response. Many modern projectors have a WiFi module. The miniaturized dimensions with wireless connectivity ensure their outstanding portability.

Additionally, these sources have a huge service life, which varies from 20,000 to 30,000 hours. For comparison, lamps usually work about 5,000 hours. On the other hand, this period corresponds to a daily 2-hour viewing for 7 years, which is more than enough given the obsolescence of the model. The power consumption and temperature of semiconductor light sources are also much lower compared to lamps. As a result, the lack of a powerful fan reduces their size and eliminates noise. But, unlike a lamp, their replacement requires contacting a service center.

Projectors with hybrid light sources (LED / Laser)

The LED light source provides low brightness of the green LED, and the laser source uses an overly expensive green laser. Some models, for example, Casio projectors, use a blue laser instead of a green LED that shines on a green phosphor. In this case, the blue laser simultaneously forms blue and green. But projector must use a rotating color wheel.

The development of digital technologies has accelerated the development of innovative technologies in almost all segments of consumer electronics. As a result, even relatively simple household appliances have become complex multifunctional devices. Of course, high-tech projectors are no exception. The modern projector has also turned into sophisticated digital device with huge media capabilities. The projector in the smartphone, miniature Pico and Cube models with semiconductor light sources perfectly illustrate this trend. Modern projectors form a projection image using DLP, LCD or LCoS technology. DLP and LCoS technologies use reflected light, while LCD works on the light pass. Of course, each of them has its pros and cons, but all of them have been successfully competing in the market for many years. However, the type of projector affects its spec and, accordingly, its choice. The first attempts to create LCD projectors began in the early eighties of the last century. In fact, the developers tried to replace the moving film and the shutter in the film projector with an LCD matrix that forms the video. A few years later, the companies has already offered the first commercial samples. Of course, these devices had many flaws. They weighed up to 20 lb with a luminous flux of no more than 300 ANSI Lm. These models had a low resolution and visualization of the grid of pixels. But they served as a prototype for the further development of large-format image reproduction technology and, as a result, the home theater segment.

LCD technology

As known, LCD technology uses the influence of electricity on the spatial orientation of liquid crystal molecules. LCD matrix uses the ability of liquid crystals to rotate the plane of light polarization under the influence of an electric current. The transparency of a polarization filter in the path of light after liquid crystals depends on the voltage. Accordingly, the light filter passes light without loss if the angle between the polarization planes of the light and the light filter is 0 ° (maximum transparency). 90 ° corresponds to the minimum transparency (the light filter passes the minimum amount of light). In fact, the LCD matrix is an array of crystals on a glass substrate, the optical transparency of which depends on the applied voltage. Of course, the LCD technology additionally uses control transistors, conductors and the corresponding color filters. In addition to LCD arrays, the 3LCD projector contains a powerful lamp, a cooling system, control electronics, a power supply unit and a lens for projecting an image. Unfortunately, the use of a single matrix did not provide the desired result due to overheating of the LCD panel, low contrast and degradation of polarizing films under the action of high temperatures. As a result, Epson developed a three-matrix projector or 3LCD.

3LCD projector

As known, DLP (Digital Light Processing) technology was developed in 1987 by a Texas Instruments Larry Hornbeck engineer based on a DMD chip. After 10 years, Digital Projection Ltd introduced the first active DLP projector. In 1998, Texas Instruments and Digital Projection Ltd received an Emmy Award for technical achievement. Today, DLP projectors successfully compete with 3LCD and LCoS models. Of course, the type of projector affects its spec and, accordingly, its choice. As a rule, most modern DLP projectors use only one semiconductor DMD (Digital Micromirror Device) chip, which forms an image using a huge number of micromirrors. This chip contains an array of micromirrors with system of their position control. For example, Full HD DMD chip contains 1920 * 1080 = 2,073,600 micromirrors. Electric signal practically instantly turns each mirror to one of two fixed positions, providing reflection of light either through the lens or onto a heat sink. Thus, each mirror reflects the light of the lamp either onto the screen or onto a heat sink of the projector, forming, respectively, a white or black dot on the screen. Multiple switching from black to white provides shades of gray on the screen.

Operation principle

Unfortunately, a 1-chip projector at a time passes only one component of a color image to the screen. A rotating wheel with color filters (color wheel) divides white light into individual colors. The color wheel is always located next to the light source. The first models rotated the color wheel at up to 3,600 rpm. But it was not enough to eliminate the rainbow effect, when the object contour acquires multicolored artifacts. Increasing its rotational speed reduces this effect. In addition, the color wheel reduces brightness. Texas Instruments has created Brilliant Color technology with a six-segment RGBRGB disk and an additional. Six-segment disk reduces the time for changing colors by half. A transparent segment increases the luminous flux, but reduces the number of gradations due to the imbalance between the brightness of black and white and color images. Too high brightness of the black and white component worsens other colors, making them darker and faded. In the future, companies experimented with the addition of intermediate colors and the area of the transparent segment. Today, manufacturers use different color configurations. Modern 1-chip DLP projectors use mainly the 6-primary colors, including Red, Blue, Green, Cyan, Magenta and Yellow. The operation principle with mirrors provides deep black and, accordingly, high contrast. But switching the mirrors is sometimes accompanied by a decrease in the number of colors gradations, reducing the smoothness of color transitions.

2-chip and 3-chip DLP projectors