DIGITAL PROJECTION TECHNOLOGIES COMPARED
This article is a major update to similar article from 2008. While the same three digital projector technologies are still being used today, as they were in 2008, each technology has evolved to provide improved performance and support new capabilities, such a 3D. This “Overview” section attempts to present a summary of the state of each digital projection technology as well as provide examples of projectors that employ each technology. The next section provides a more detailed, more technical, discussion of the three digital projection technologies as well pointing out the areas in which each technology excels and where each has performance limitations. The final two sections discuss projector placement considerations and a observations related to a few specific projector performance factors.
This article covers projectors used for business, education and home theater applications, with a emphasis on the latter category, and the underlying digital imaging technologies being used. These digital imaging technologies include Digital Light Processing (DLP), Liquid Crystal Display (LCD), and Liquid Crystal on Silicon (LCoS). The following provides a high level overview of each of these technologies and provides examples of projectors using each of these technologies. More detailed information for each of these projection technologies is provided later in this article.
I would like to offer a few observations as to certain features now available, or soon to become available, on digital projectors that may influence you future decision for a projector purchase. Such features not unique, or need not be unique, to DLP, LCD or LCoS digital projection technology:
Dynamic irises first came into general use with LCD projectors as a means for improving on these projector’s relatively low native on/off contrast ratio and elevated black levels. Dynamic irises can now be found in many home theater projectors using DLP, LCoS and 3LCD digital display technologies including those with a relatively good native contrast ratio and low black levels. One notable exception is JVC who, with their industry leading native on/off contrast ratios of up to 100,000+, have avoided use of dynamic irises in their D-ILA (LCoS) projectors.
A more recent development is dynamic control of the projector’s lamp to facilitate increase light output in 3D mode. Sony is now using this technique within certain of their SXRD (LCoS) projectors. This feature may show up in other projectors in the future.
The migration from lamps to solid state light sources (i.e., LEDs and Lasers) has become widespread with the small portable projector’s use of LED light sources.
- LED light sources have more recently found their way in a few larger business and home theater class projectors, but these are generally limited to only moderate light output.
- The use of lasers is currently in far more limited use than LEDs. There are currently a few hybrid DLP business projector models, such as the Panasonic PT-RZ470, that are using LEDs for the red and blue primary colors and with a laser used excite a phosphor target, which in turn emits a green light (i.e., the third primary color). This hybrid approach is being used as it is difficult to produce green LEDs with enough light output to match what is practical for the red and blue LEDs. This hybrid technique may very well migrate to future home theater projectors.
- Sony now offers a business projector that uses a blue laser to excite a phosphor target that in turn emits a white light. This projector has a fairly high light output (rated at 4000 lumens) and it appears the Sony white light laser/phosphor approach can be used more-or-less in updated versions of existing projector designs whose light engine were originally designed around lamp-based light sources. This approach seems to have some advantages from a cost point of view and will likely be used in future projector models, perhaps including those intended for home theater use.
- Multiple companies have demonstrated engineering models of projectors that use red, blue and green lasers to individually illuminate the digital imaging chips assigned respectively for the red, blue and green colors. There are both technical and regulatory issues that must be overcome before such direct use of lasers (i.e., not simply limited to exciting a phosphor target) can gain wide-spread use in projectors intended for the business, education or home theater market.
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