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

Christie H Series 1DLP

It is not easy to choose a projector if we are not clear about what we need it for. Reproduced on specification sheets, many of the projectors seem 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., which can 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: single-chip and three-chip.

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 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 with your application you are looking for data projection or if what you want is the viewing of videos, or both.

LWU701-D-142 LCD

The 'abc' of DLP

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

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

On its own, the image that forms the DLP chip looks black and white. To produce color images, two methods are usually used: one-chip or three-chip. The latter uses a DMD for each primary color (red, green, blue) that converge optically to produce a single image.

the single-chip approach is limited to using a dlp chip and usually places a high-speed spinning disk between the dmd chip and the lamp called a color wheel.

L2K1000 LCD

The color wheel is divided into several sectors, each of which contains a color filter. The minimum will be a red one, one blue and one green. Some projectors add a white segment to boost light production, 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 quick succession, the DLP chip in a cycle that repeats several times per second. The image displayed on the DLP chip also completes information cycles between the red, green and blue in sync with the wheel. The colors cycle at a high enough speed that the eye perceives 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 cycle the colors., performing that task electronically.

Christie and NiallFerguson Ideas Screening

Principles of LCD

LCD projectors use small liquid crystal panels that, rather than reflecting 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 from the lamp into the three colors (red, green and blue) then channeling them through their respective panels. The image is formed on a panel altering an electrical signal (voltage) sent in quick 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 resulting images are projected in the same place on the screen.

Christie H Series 1DLP

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 going to show mainly. Will it consist mostly of data for presentations?, in video playbacks, or in a combination of the two?

Both single-chip DLP projectors and LCDs are suitable for both types of content. However, if our main need is the projection of data we will want to have the greatest 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.

Yes, on the contrary, our needs are focused on video projection, the colour reproduction must be impeccable, so the difference between a single-chip DLP projector and an appropriate LCD model will be minimal.

Christie projectors at Imginarium

Image quality

Today, and within a similar price range, there isn't much difference in image quality or brightness between a single-chip DLP projector and an LCD projector. That said., follow a few distinctive features that should be known:

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

The typical commercial or business presentation may demand more brightness in 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 indispensable requirement in video projection.

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

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

Conference room iGuzzini Christie projectors

Color cycle speed: in the case of the DLP of a chip, 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 mainly for video viewing.

That's why, some viewers perceive in the image fleeting multicolored traces (rainbow) in the case of bright objects, especially when those objects are in motion. However, the perception of these artifacts varies from person to person.

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 of the visual acuity of the image, something that, even if it doesn't matter too much in a presentation, can be essential when watching a video. Hence DLP images are considered more 'cinematic' than LCD images..

Lack of convergence: lack of convergence is the term for an effect that you may have noticed in an LCD image: color stripes 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.

On the other hand, one-chip DLP projectors have been designed with a single image-creating chip that displays all three colors sequentially, so with a DLP projector of a chip we will be free of the problem of lack of convergence.

LWU501i LCD

What about reliability?

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

In the past, projector LCD panels could fail due to a progressive decomposition of ultraviolet light (Uv) that is filtered by the lamp.

A new technology that operates within the LCD panel itself, called inorganic alignment layers, 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 in applications 24/7.

An LCD problem is that of image retention. If an LCD projector or flat panel displays a static image for an extended period of time, LCD tends to maintain a post-image effect, a kind of ghost image of that static image, that 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 (continuous), which accentuates the odds of image retention. When an operation is required 24/7 the DLP projector option is much more advisable.

Christie DHD600-G 1DLP

Single-chip DLP

In the case of DLP, we might think that a DMD chip full of moving mirrors is, in itself, unreliable for its mechanics and movement. However, even though mirrors are movable elements, they are so tiny that the forces involved in their movement are insignificant.. Tests carried out over many years have shown that DLP chips are highly reliable and long-lived..

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

Another traditional concern generated by lamp-based single-chip DLP projectors is that derived from the motor that rotates the color wheel.. It is an engine similar to those of hard drives and have proven to be highly reliable.

When we refer to reliability, Another aspect to keep in mind is that the products of a chip have sealed optics, which helps to eliminate the possible contamination of the panel that usually manifests itself on the screen in the form of dark spots and / or chromatic distortion. On the other hand, 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 using one or the other technology tend to be similar in performance and performance 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-, 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.

Mark-Fernandez-ChristieMark Fernandez

Director of Christie for Spain and Portugal

 

 

 

 

 

 


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by • 9 sep, 2015
• section: projection, Grandstands