Projectors have come a long way from the early days. The technology being utilized in projectors from different brands is constantly evolving. One of the biggest changes that have been seen is the way the projectors produce images. There are primarily three different technologies being used in projectors – DLP, LCD, and LCoS. They all produce images using different methodologies.
Digital Light Processing (DLP)
The Digital Light Processing technology is the most commonly used technique in projectors. A DLP projector has an array consisting of many small square mirrors known as the Digital Micromirror Device or the DLP chip. The mirrors can independently reflect the light produced by the projector lamp. The number of mirrors will depend on the resolution of the projector. Each mirror represents one pixel produced by the projector. A 1080p projector has over 2 million mirrors (1920 multiplied by 1080 to be exact).
The direction in which the light is reflected by a mirror determines the creation of the pixels on the screen. Each mirror is mounted on a hinge and its position can be adjusted independently. The mirror can be tilted either towards the light source or away from it at an angle ranging from +12° to -12°. If the mirror faces towards the light, it creates an “on pixel” which is light in color, if it faces away it creates an “off pixel” which is dark in color. The projector may adjust each mirror thousands of times in one second. The position of each mirror depends on the image code that the DLP chip receives. The chip adjusts the image by optimizing features like brightness and color of the image and then passes the adjusted image code to the mirrors.
The mirrors create the image by reflecting the light from the lamp onto the projector screen via the lens. The light reflected by the mirrors is in a gray shade. The pixels reflected can be in one of the 1024 different shades of gray color that the projector supports, yielding a grayscale image with high details. The projector adds color to the image by using a spinning transparent color wheel.
The color wheel is also in sync with the DLP chip. It converts the white light from the lens into red, green or blue color before it falls on the mirrors as per the directions of the DLP chip. The color wheel and the mirrors work in tandem with the DLP chip and can create 16.7 million colors. The eyes of the viewers will blend different colors and allow them to perceive the image as it should be. The mirror will repeatedly flash red and green light on a pixel if it needs to make it yellow. As the flashing speed is very fast, the eyes of the viewer will perceive the image as yellow.
Some projectors, especially those used in movie theatres, make use of three DLP chips each of which has a separate color wheel. They also have a prism that separates the white lights from the lens into red, green and blue. Each of the three chips receives light of a different color and reflects it onto the mirrors. It allows the projector to produce up to 35 trillion colors. Modern projectors use LEDs instead of the color wheels and lamps traditionally used in the projectors. These LEDs are red, green and blue and produce superior images.
Liquid Crystal Display (LCD)
The Liquid Crystal Display (LCD) is another technology being used in projectors to produce images. LCD projectors function in a way similar to the LCD TVs.
The projectors have a light source which emits white light. This beam of light is separated into three distinct wavelengths, red, green and blue, by using dichroic mirrors. The projector has three liquid crystal panels each of which is made up of tiny pixels depending on the resolution of the projector. The pixels are colorless and don’t alter the wavelength of the light. An electric current can control the pixels and determines if the light will pass through a pixel or not.
All the three LCDs in the projector display the same image at a particular instance of time. The images on the LCDs are in grayscale. The three separated light beams hit one of the three LCDs imparting color to the grayscale image. There are three versions of the image produced; the first is red, the second green and the third has a blue tint.
These three versions of the image are then combined into one image via a dichroic prism which is made up of four triangular prisms. The resulting final image consists of millions of colors. This final image is then passed through the lens and onto the projector screen.
Liquid Crystal on Silicon (LCoS)
The LCoS projectors combine the technologies of the DLP and the LCD projectors. These projectors have liquid crystal chips like the LCD projectors, but there is a significant difference. The chips used have a reflective surface on their backside which allows them to reflect light like the mirrors in DLP projectors.
In the LCoS projectors, the beam of white light from the lens is filtered into visible components and then divided into red, green and blue wavelengths. The three beams of different colors are then directed onto the three LCoS chips respectively.
An LCoS chip comprises of a transparent thin-film transistor layer, followed by a liquid crystal layer and a semiconductor layer made of silicon in the end. The semiconductor layer is pixilated and has a reflective surface. The light first hits the transparent layer and then reaches the liquid crystal layer. The liquid crystal layer controls the amount of light that goes onto the semiconductor’s surface depending on the image that has to be output. The semiconductor layer then reflects the light.
The light from each of the three LCoS chips is then combined using a prism to produce the final image. The lens then projects this image onto the projector screen.
How do the DLP, LCD and LCoS projectors stand against each other?
The pros and cons of the three variants of the projectors must be taken into consideration to determine how they fare against each other.
The contrast ratio of a projector is one of the most important features that determine its picture quality. It is defined as the difference between the darkest pixel and the whitest pixel output by the projector. It imparts depth and dimension to the images displayed on the projector screen. The higher is the contrast ratio of a projector the more realistic the images will appear.
Modern DLP projectors have a better contrast ratio when compared to the LCD projectors. The images output by them are far more realistic than those produced by the LCD projectors. Hence, DLP projectors are highly recommended for home theatres. Companies have been continuously improving and refining the technologies used in LCD projectors. Most modern LCD projectors offer good contrast ratio though not as good as DLP and LCoS projectors.
LCoS projectors have the best contrast ratio as they utilize the technologies of both DLP and LCD projectors. It allows the projectors to produce images that are as real as possible. Some projectors use the Auto Iris technology to boost the contrast ratio. The lens opens when more light is needed and closes in dark scenes when a low amount of light is required. It can improve the contrast ratio of the projector, but all buyers may not prefer it.
The brightness of a projector is another important feature that buyers consider while searching for a projector. The brightness of a projector defines the light output by the projector and is called the lumens rating.
While the light output of a projector varies from one model to another, DLP projectors on an average have the best light output. When considering lamp and LED DLP projectors, the lamp DLP projectors will be brighter though modern LED DLP projectors are almost as good as the lamp DLP projectors.
The light output of the LCD projectors is less than the DLP and the LCoS projectors though it will vary from one model to another. LCoS projectors have not traditionally been as bright as the LCD or DLP projectors. However, technological advancements have put the brightness of modern LCoS projectors at par with the DLP projectors if not better than them.
Another thing that will impact the light output of the projectors is their cost. An entry-level DLP projector may have a lower lumens rating than a top-end LCoS projector due to the quality of the components used. Also, an entry-level LCD model will have a lower light output than a top-of-the-line model. While comparing the brightness output of different types of projectors, it is best to consider models within the same price range.
The color range output by a projector determines how vibrant the image will be. Due to constant advancement in technology, all the three types of projectors produce images with comparable colors. It may, however, differ from model to model or brand to brand, and a buyer can browse multiple models for the same.
Buyers who want to buy a projector for their home theatres or for playing video games have to consider if the images have motion blur. Motion blur is the streaking effect observed in videos that have rapidly moving objects. The transition of the objects in the video is not smooth and appears blurrier. It can hamper the viewing experience of the user.
DLP projectors have the least amount of motion blur and hence produce the sharpest and well-detailed images. LCD and LCoS projectors do experience a certain level of motion blur especially in videos with rapidly moving objects. However, very few people find a noticeable difference between the projectors.
A nuance that some people might notice in projectors is the rainbow effect. A rainbow effect causes the bright part of images produced by a projector to have a hint of multi-colored light like a smeared rainbow.
The effect is seen in single-chip DLP projectors and happens when the speed of the color wheel used on the projector reduces while producing images. LCD and LCoS projectors do not use a color wheel and hence do not produce the rainbow effect. The rainbow effect is not seen in three-chip DLP projectors and is minimal in single-chip projectors with high-speed color wheels.
Screen Door Effect
Another nuance that viewers may see in the images produced by the projectors is the screen door effect. All projectors produce images that are composed of pixels. When the images produced by projectors are viewed from a close distance, the pixels might be visible on the screen with spaces in between. The phenomenon is called the screen door effect.
The screen door effect in DLP projectors is almost invisible as compared to the LCD projectors. They have a higher pixel fill factor which implies that the space between simultaneous pixels is less making the effect inconspicuous. LCoS projectors have the least pronounced screen door effect as compared to DLP and the LCD projectors. Buyer can consider projectors with higher resolution to mitigate the screen door effect. The higher is the resolution of the projector, the less will be its screen door effect.
The upkeep of the projectors is another important factor to consider when buying a projector. Projectors are exposed to dust particles which can accumulate over time and hamper the image quality.
The DLP projectors are the best choice for dusty environments as they have sealed chips which makes them dust resistant. The image quality of the projector does not decay over time ensuring that they have low upkeep.
The LCDs used in LCD projectors are prone to dust particles as they are not completely sealed which may cause the image quality to degrade over time due to the accumulation of dust particles.
LCoS projectors may have sealed or open chips depending on the model. Their dust resistance will depend on whether the dust can reach the path that the light beam travels through or not.
Projectors that use multiple DLP chips or LCDs need to converge the light beam from three sources for producing the final image. As the chips are small, they have to be perfectly aligned as even a slight variation can affect the final image quality. LCD, LCoS, and triple-chip DLP projectors are the ones that can have convergence issues. Not every projector model will have convergence issues. It is seen in projectors that might have suffered an accidental fall in transit or when in use. Convergence issues are not seen in single-chip DLP projectors as they use a single chip and have no need of convergence.
A few Other Notable Differences Among the DLP, LCD and LCoS Projectors
1) The DLP projectors are lightweight as compared to LCD and LCoS projectors making them the ideal choice for customers who are looking for a portable option. LCoS projectors are the heaviest among all three types of projectors.
2) The DLP technology produces the deepest black color among all the projection techniques. However, their contrast ratio is not as good as LCoS projectors. The black color that is produced by LCoS projectors is not as dark as that produces by the DLP projectors but they have the best contrast ratio that counters it.
3) The LCDs employed in the projectors may have a buildup of dust particles over time which will lower the quality of the output images and cause them to appear smudged. These projectors must be protected from dust and have high upkeep.
4) The pixels of the LCDs can also burn overtime and reduce the quality of the output images. DLP and LCoS projectors do not face the pixel burn issue.
5) LCoS projectors are the most expensive among the three types of projectors while the DLP projectors are the cheapest when considering projectors with the same resolution and features.
The right projector for a buyer will ultimately depend on his or her requirements and budget. What may be the right projector for one user might be an inappropriate choice for another user. Buyers can browse and try different projectors for determining the one that is perfect for their needs.