3LCD, DLP, and LCoS - How These Three Projection Techologies Compare in Home Theater Projectors
6/7/2008 - Art Feierman
For an older article that also looks at DLP vs 3LCD projectors relating to business projector issues: DLP vs LCD Projectors
This article is long overdue. My last writings on this topic were over two years ago, and, at that time, home theater projectors were pretty much limited to three basic groups: 3LCD projectors, single chip DLPs, and the far more expensive 3 chip DLP projectors.
Since 3 chip DLP projectors are far more expensive than the others, the real discussion two years ago, was between the single chip DLP's and the LCD - that is, 3LCD projectors.
At that time, DLP projectors were definitely considered the performance leader, at least in one critical area - true contrast, and the resulting better black levels than 3LCD.
And there really weren't any significant, affordable LCoS projectors, just a very expensive Sony, well over $10,000.
Today, LCoS technology, is arguably the best of the three technologies in the under $10,000 home theater projector arena. Certainly, they aren't the cheapest, with all the LCoS action (for all practical purposes) being 1080p projectors, so LCoS is definitely not competing on the low end (720p resolution projectors).
Another important point, is that technologies such as dynamic irises and dimmable lamps, which, two years ago, were pretty much limited to 3LCD projectors as they used "technology" to offset the DLP projectors' advantage in black levels and contrast. Today, many of the DLP projectors and LCoS projectors also have added dynamic irises, etc., to further improve their performance.
The Basic Differences in Technologies
I'm not going to go into the finer points of the design and workings of each technologies, but do need to lay down the basics.
DLP Projectors (single chip). These projectors can easily be the smallest projectors as they are the only single chip technology. LCoS and 3LCD (like three chip DLP's) require a bigger box. Consider: With a single chip DLP, you start with a light source, bounce light off of the DLP chip, and ultimately, out the lens, to the screen.
With 3LCD, you still start with the light source, but you must split it into 3 beams, one each for red, green and blue, the primary colors. Once the light is split, mirrors send the beams to different locations inside the projector box. At that point, the light passes through one of the three LCD panels. These panels are not colored, but grayscale, but each has a different color filter. The end result, when light passes though them, is three beams - red, green, and blue. Each of these beams then passes through a dichroic prism, which recombines the three beams into a single full color beam.
With LCoS, (no matter what the manufacturers call it (Sony uses SXRD, JVC uses D-iLA, Canon calls theirs Aisys, etc.), the process is similar to 3LCD, in that you start by splitting the light into three beams. A key difference, though, is that LCoS (Liquid Crystal on Silicon) is a reflective panel (like DLP) rather than transmissive (light passes through it), like the 3LCD panels.
So, light bounces off of the LCoS panels, then to a dichroic prism (like 3LCD) to recombine the light into a single, full color image.
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Other aspects - DLP projectors claim a sealed light path - that is, dust cannot get into the system to end up on the DLP chip, or other surfaces in the light path. This is also true for most LCoS projectors. 3LCD, however is not sealed, that is air does blow past the panels, and dust landing on them, can cause a dust blob, that can be visible in dark scenes. Fortunately dust blobs are not a common problem, but worth mentioning (most - if not all, 3LCD manufacturers will treat a visible dust blob, as a warranty issue, and clean the projector under warranty. That said, it is another reason that a long warranty is a beneficial thing.
OK, so that covers the really basic differences. Read on for other traits of each technology.