What's the Difference: LCD vs. DLP Pt. 1

LCD or DLP? This is a great debate that has raged on for years. Some of the debate is fueled by technology, 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. But we’ll 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. 

Image courtesy of Christie Digital

Image courtesy of Christie Digital

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’re all open) is produced. 

DLP is all Smoke and Mirrors

Well, technically no smoke. Unless you count the magic smoke that all electronics run on. Let the magic smoke out, and they stop working. But I digress. Below you’ll see an image of a typical single-chip DLP engine. As you can see, it’s a bit more complex. DLP stands for Digital Light Projection, and was developed by Texas Instruments. It’s 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’s a single chip, there is a color wheel in the system to produce the various colors.

Image courtesy of Christie Digital

Image courtesy of Christie Digital

The technology takes advantage of a phenomenon in our vision called persistence of vision. Our eyes see relatively slowly. And what we see tends to stay there for a little bit. The DLP engine will flash the red portion of the image on the screen and sometime between 1/60th and 1/240th of a second later will then flash the green portion. Then the blue, then back to red. Some projectors event throw in yellow, magenta and cyan for good measure. In that short time frame, the red doesn’t full fade away—at least in our eyes. So when the green and blue parts pop up, we see it as one color. It’s crazy, but it works.

The downside is that some people have faster vision than others and can actually see each color individually. This is called the rainbow effect. It’s less of a problem now than it used to be; companies have sped up the rotation of the wheel to mitigate the effect. But if you can see it, you can’t un-see it, so to speak. 

3-Chip DLP is the Same, Only More

A 3-chip DLP projector is very similar to a single-chip, only there are three; one for red, green and blue. The rainbow effect doesn’t come into play in a 3 DLP design because there is no spinning color wheel. When you look at the above diagram, you can see why 3 DLP designs are so expensive; there’s a lot of stuff going on in there. You do get a good-looking image out of all the complexity, however. 

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 the me the answer is yes. And no. 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 doesn't matter. However, there are pros and cons for each technology, and one may be better suited for your application than the other. We’ll talk about that next time.

Roland

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