Single-chip DLP or LCD projection technology, what is the ideal option?

Choosing between these two projection technologies is not always easy. The director Marcos Fernández, Christie's director for Spain and Portugal, This Tribune provides detailed information to choose the best option for each application..

It is not easy to choose a projector if we are not clear about why we need it. Reproduced on specification sheets, many of the projectors look more or less the same to us. 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, it could be LCD (liquid crystal display), LCoS (liquid crystal on silicon) o DLP (digital light processing). As if that were not enough, DLP itself presents two varieties: one-chip and three-chip.

Three-chip DLP is widely considered the 'best of the best' in terms of image quality and projection standards.. However, In the case of applications that do not seek the maximum in any specific aspect of operation, single-chip DLP models or LCD technology are usually sufficient.. In this article we offer information aimed at helping you choose between the two technologies, Whether you want to project data with your application or watch videos, or both.

The 'abc' of the DLP

All DLP projectors have a DMD chip inside. (digital micromirror device) covered with square mirrors of microscopic size, with a mirror for each pixel of the projected image.

All mirrors rotate between two different angles: an angle that reflects light from the projector lamp through the screen lens, generating a bright pixel when doing so; and another angle that reflects the light and away from the lenses towards an internal element that absorbs the light, producing a dark pixel on the screen. To show an intermediate gray tone, All mirrors rotate at high speed between both angles thousands of times per second..

alone, the image formed by the DLP chip is seen in black and white. Two methods are usually used to produce color images.: the one with one chip or the one with three chips. The latter uses one DMD for each primary color (rojo, verde, azul) that converge optically to produce a single image.

The single-chip approach simply uses a DLP chip and typically places a high-speed spinning disk called a color wheel between the DMD chip and the lamp..

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 light output, and others incorporate yellow, cyan and/or magenta.

Added in various combinations, The three colors generate rich and colorful images. When you turn the wheel, each color illuminates, in quick succession, the DLP chip in a cycle that repeats several times per second. The image displayed on the DLP chip also cycles information between red, green and blue in sync with the wheel. Colors cycle at a speed high enough for the eye to perceive the image in full color..

Some single-chip DLP projectors use, instead of lamp, Led (light emitting diodes) or a combination of Led and laser. Some of these models do not require a color wheel to carry out color cycles., performing that task electronically.

LCD Principles

LCD projectors use small liquid crystal panels that, more than to reflect light, They have been designed to transmit it. Three panels are generally used, one for each color. Some projectors use a fourth panel to improve color reproduction.

Optical filter components inside the projector divide the white light from the lamp into the three colors (rojo, green and blue) then channeling them through their respective panels. The image is formed on 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 panels, green and blue 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 consider what type of content we are mainly going to show.. Will it mostly consist of data for presentations, in video views, or a combination of the two?

Both single-chip DLP and LCD projectors are suitable for both types of content. However, If our main need is data projection we will want to have the highest brightness we can afford with a given budget. In that sense, a single-chip DLP projector designed for fixed installations will probably be the best option.

And, on the contrary, our needs focus on video projection, color reproduction must be impeccable, so the difference between a single chip DLP projector and a proper LCD model will be minimal.

Image quality

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.. That being said, There are a few distinctive characteristics that should be known.:

Color reproduction: all projector designs sacrifice brightness for the depth of projected colors, or the opposite. The choice of one aspect inevitably goes to the detriment of the other. The result is that some projectors have deeper or more accurate color than others., depending on what your applications are.

The typical business or commercial presentation may require more brightness under certain ambient lighting conditions; instead, If what we need is to review data or brand standards, Color accuracy becomes a priority, which also becomes an essential requirement in video projection.

As a rule, LCD projectors fall somewhere in the middle, showing acceptable colors in relation to the brightness they project, while those intended mainly for video viewing sacrifice some light projection for the sake of better chromaticism..

Single-chip DLP projectors cover a wider spectrum, ranging from models for presentations with colors simply appropriate to their function, to models with great color quality designed for video. Some single-chip DLP projectors offer the option to select optimal brightness or greater color accuracy in playback settings.

Color cycle speed: in the case of single-chip DLP, The speed of the color cycle may vary depending on the projector as well as, in some cases, depending on software configurations. In models for presentations the speed of the color cycle tends to be slower than in those intended primarily for video viewing.

For this reason, some viewers perceive fleeting multicolored traces in the image (rainbow) in the case of shiny objects, especially when those objects are in motion. However, the perception of these artifacts varies according to people.

Pixel Visibility: LCD projectors have a greater distance between pixels than DLP projectors, a circumstance that makes the separation more visible with the consequent reduction in the visual acuity of the image, something that, although it is not very important in a presentation, can be essential when watching a video. Hence, DLP images are considered more 'cinematic' than LCD images..

Lack of convergence: Deconvergence is the term for an effect you may have noticed in an LCD image: some stripes of color in horizontal and vertical lines. The effect appears when the alignment that the images of the three LCD panels must maintain with each other is not precise enough. And although manufacturers do everything possible to minimize it, Lack of convergence continues to affect some LCD projectors.

Besides, Single-chip DLP projectors are designed with a single image-creating chip that displays three colors sequentially., so with a single chip DLP projector we will be free from the problem of lack of convergence.

What about reliability?

Reliability is as important as performance, and the two technologies, One-chip LCD and DLP, They work well in that regard..

In the past, LCD panels in projectors could fail due to progressive decay of ultraviolet light (UV) that leaks through the lamp.

A new technology that operates within the LCD panel itself, called inorganic alignment layers, It has been an important advance by increasing the protection of LCDs against damage caused by ultraviolet light., despite which, This solution is still not the most suitable for applications 24/7.

An LCD problem is image retention. If an LCD or flat panel projector displays a static image for an extended period of time, the LCD tends to maintain an after-image effect, a kind of ghost image of that static image, which remains visible with the new content already on screen.

Most LCD manufacturers warn of the risk of this type of operation., a problem that can be especially serious in applications that require operation 24/7 (continuo), which increases the chances of image retention. When operation is required 24/7 The DLP projector option is much more advisable.

One chip DLP

In the case of DLP, We might think that a DMD chip full of moving mirrors is, per se, unreliable due to its mechanics and movement. However, even though the mirrors are movable elements, They are so tiny that the forces involved in their movement are negligible.. Tests carried out over many years have shown that DLP chips are highly reliable and long-lasting..

A key advantage of DLP technology is that, rather than internally absorbing light in the imaging device to produce black, mirrors simply redirect light to an internal light 'absorber', reducing thermal stress on the imaging device (DMD) considerably increasing its life cycle.

Another traditional concern generated by lamp-based single-chip DLP projectors is the motor that rotates the color wheel.. It is a motor similar to those used in hard drives and has proven to be highly reliable..

When we refer to reliability, Another aspect to take into account is that single chip products have sealed optics, which helps eliminate possible contamination of the panel that usually manifests itself on the screen in the form of dark spots and/or chromatic distortion. Besides, It is not uncommon for LCD projectors to require cleaning service.

In conclusion, single-chip DLP projectors and LCD projectors offer great value in a wide range of applications. In a given price range, Products that use one or another technology tend to be similar in performance and operating results..

However, although there are fundamental differences between the two technologies, there are applications that, depending on the content - data or video, image quality and reliability-, They fit one better than the other.. In this article we have summarized the most relevant information to help you choose the best option for your application needs..