Written by Mike Sessler
LCD or DLP? The debate between the two has raged on for years. Technology fuels some of the debate, much more is fueled by marketing. Thankfully, manufacturers in both camps have been steadily improving their respective technologies over the years, and the difference is now smaller than ever. I believe for most applications, the technology inside the projector is now less important than the service, support, price and brightness; and the suitability for the application. However, we will get to that shortly.
Much has been written about this subject, and rather than attempt to rehash all of that; I'm going to give you an overview of the two technologies along with some links to learn more. Let's start off with a basic overview of how the two methods produce a picture. In reverse alpha order, LCD first.
All LCD Projectors are 3 Chip Designs
LCD stands for Liquid Crystal Display. You may see some projectors labeled 3LCD or being touted as having three chips as opposed to 1. The marketing difference compares not to single-chip LCD projectors (there are none), but to single-chip DLPs—the primary competitor to LCDs. Below is an example, albeit a highly simplified one, of how an LCD projector produces an image.
The light from the bulb(s) is split into three parts. It passes through three LCD panels (red, green & blue), and then re-combined. The result is a color image. The LCD panel has millions of pixels that can be open, closed or partially open. When open, light passes through, and a color (or white if they are all open) is produced.
DLP is all Smoke and Mirrors
Well, technically no smoke; however, I digress. Below you will see an image of a typical single-chip Digital Light Projection (DLP) engine. As you can see, it is a bit more complex than an LCD engine. DLP was developed by Texas Instruments and is essentially a chip full of thousands of little mirrors. The mirrors tilt either toward or away from the lens producing light or not. Because it is a single chip, there is a color wheel in the system to create the various colors.
The technology takes advantage of a phenomenon called persistence of vision. Our eyes see relatively slowly. Moreover, the image of what we see lingers for some time. The DLP engine will flash the red portion of the image on the screen and between 1/60th and 1/240th of a second later will flash the green portion. Then blue, then back to red. In that short time frame, the red does not entirely fade away—at least in our eyes. So when the green and blue portions flash, we see it as one color. Surprisingly, it works. Thanks, physics!
The downside is that some people have faster vision than others and can see each color individually, this is known as the rainbow effect. This is less of a problem now than it used to be; companies have sped up the rotation of the wheel to mitigate the effect. However, if you can see it, you cannot un-see it, so to speak.
Does It Matter?
One of the questions I always ask when evaluating competing technologies is, "Does it matter?" When it comes to LCD vs. DLP, for me the answer is yes. The technology has advanced to a point where at a given price point, either will produce an acceptable image. So to some extent, the answer is no, it does not matter. However, there are pros and cons for each technology, and one may be better suited for your application than the other. We will talk about that next time.
Images courtesy Christie Digital