Choosing between these two projection technologies is not always easy. The director Marcos Fernandez, director of Christie for Spain and Portugal, provides in this detailed Tribune information to choose the best option for each application.
It is not easy to choose a projector if we do not have a clear idea why we need it. Reproduced on specification sheets, many of the projectors look more or less the same. However, their operation and the quality of the image they produce can make them totally different.
The fundamental reason for these differences lies in the technology on which they are based, which may be LCD (liquid crystal display), LCoS (liquid crystal on silicon) or DLP (digital light processing). To make matters worse, the DLP itself has two varieties: a chip and three chips.
The three-chip DLP is widely regarded as ‘the most of the most’ in terms of image quality and projection standards. However, in the case of applications that do not pursue the maximum in any aspect of concrete operation is usually enough with DLP models of a single chip or LCD technology. In this article we offer information aimed at helping you choose between the two technologies, whether with your application you are looking for data projection or if you just want to watch videos, or both.
The ‘abc’ of the DLP
All DLP projectors have a DMD chip (digital micro mirror device) covered in square mirrors of microscopic size, with one mirror for each pixel of the projected image.
All the mirrors rotate between two different angles: an angle that reflects the light of the projector’s lamp through the lens of the screen, generating a bright pixel; and another angle that reflects the light and moves it away from the lenses towards an internal element that absorbs light, producing a dark pixel on the screen. To show an intermediate gray tone, all the mirrors rotate at great speed between both angles thousands of times per second.
By itself, the image that forms the DLP chip is seen in black and white. To produce color images usually resort to two methods: the one of a chip or the one of three chips. The latter uses a DMD for each primary color (red, green, blue) that converge optically to produce a single image.
The focus of a single chip is limited to using a DLP chip and usually placed between the DMD chip and the lamp a disk that rotates at high speed and is called a color wheel.
The color wheel is divided into several sectors, each of which contains a color filter. The minimum will be one red, one blue and one green. Some projectors add a white segment to boost the production of light, and others incorporate yellow, cyan and / or magenta.
Added in various combinations, the three colors generate rich and colorful images. When turning the wheel, each color illuminates, in rapid succession, the DLP chip in a cycle that repeats several times per second. The image shown on the DLP chip also completes information cycles between red, green and blue in synchronization with the wheel. The colors perform their cycles at a high enough speed so that the view perceives the image in full color.
Some single-chip DLP projectors use, instead of a lamp, LEDs (light-emitting diodes) or a combination of LEDs and lasers. Some of these models do not require a color wheel to perform the color cycles, performing this task electronically.
Principles of the LCD
The LCD projectors use small liquid crystal panels that, more than to reflect the light, have been designed to transmit it. Usually three panels are used, one for each color. Some projectors use a fourth panel to improve color reproduction.
The optical filter components located inside the projector divide the white light of the lamp into the three colors (red, green and blue) then channel them through their respective panels. The image is formed in a panel by altering an electrical signal (voltage) sent in rapid succession to each pixel.
The result is the transmission of light through the LCD panel, creating a bright pixel on the screen; or the absorption of light by the panel, generating a dark pixel on the screen. The red, green and blue panels surround a prism that ensures that all the resulting images are projected in the same place on the screen.
A chip vs. LCD: data or video content?
When choosing a projector for a specific application it is important to ask ourselves what type of content we are going to show mainly. Will it consist mainly of data for presentations, video reproductions, or a combination of both?
Both single-chip DLP projectors and LCD projectors are suitable for both types of content. However, if our main need is the projection of data we want to have the highest brightness that we can afford with a given budget. In that sense, a DLP projector of a chip designed for fixed installations will probably be the best option.
If, on the other hand, our needs are focused on video projection, the color reproduction should be impeccable, so the difference between a DLP projector on a chip and an appropriate LCD model will be minimal.
Currently, and within a similar price range, there is not much difference in image quality or brightness between a single-chip DLP projector and an LCD projector. Having said that, there are a few distinctive characteristics that should be known:
Color reproduction: all projector designs sacrifice brightness in favor of the depth of projected colors, or otherwise. The option of one aspect inevitably detracts from the other. The result is that in some projectors the color is deeper or more precise than in others, depending on what their applications are.
The typical commercial or business presentation may require more brightness in certain environmental lighting conditions; on the other hand, if what we need is to review data or brand standards, the precision in the color becomes a priority, which also becomes an indispensable requirement in the video projection.
In general, LCD projectors are placed on a medium term, showing acceptable colors in relation to the brightness that they project, while those that are mainly used for video viewing sacrifice some light projection for the sake of a better color scheme.
DLP single-chip projectors cover a wider spectrum, ranging from models for presentations with colors simply suited to their function, to models with high color quality designed for video. Some single-chip DLP projectors offer the option of selecting optimum brightness or color accuracy in playback settings.