There are two main competing technologies in digital projectors: LCD and DLP. DLP projectors reflect light off the image panel while LCD projectors use light passing through colored panels to project its image. These technologies are different, yet the result is amazingly similar.
This article is written from the perspective of considering a DLP projector in a possible purchase. These are the things one should know about DLP projectors so that they can understand the differences between DLP technology and LCD technology. There is another article about the advantages and disadvantages of LCD projectors which gives more information from the LCD perspective.
DLP Projector Advantages
DLP, which stands for Digital Light Processing, is a technology from Texas Instruments. It uses mirrors and a color wheel to reflect and filter light that gets projected. For home and business use, DLP projectors use one reflective light panel for all three colors. For digital cinemas there are three panel DLP projectors which cost $10,000 and up. Most people will only have experience with the single-panel variety of DLP projector.
Typically DLP projectors are smaller and quieter than LCD projectors. There are several sub-three pound projectors on the market that are DLP. Currently there are no LCD projectors that weigh less than three pounds.
One of the biggest talked about advantages of DLP over LCD is the superior contrast ratio. Contrast ratio is the number of steps from a black section of an image to a white section. This is appreciated more in a home theater than a business conference room. Many DLP projectors today have a contrast ratio of 50000:1. Just a few years ago a contrast ratio of 3000:1 was considered good. This advantage over LCD is lessening today as LCD technology has begun to catch up with DLP in contrast ratio.
Because most of the DLP projectors in common use are of a single mirror variety, there are no problems of an image falling out of alignment. It is possible with multi-panel DLP and LCD projectors to have one of the image panels become misaligned over time. This causes either ghosting or a softening of the image focus. These types of problems are called convergence problems.
DLP projectors have a sealed image mirror. This means that dust cannot get into the DLP chip system as is possible with LCD projectors. Because of the sealed DLP chip, there is less maintenance needed. Air filters, which can become clogged causing overheating in an LCD projector, are non-existent in a DLP projector. A lack of heat buildup in a DLP projector means that the projector lamp will not die prematurely. The downside of not having air filters is that the other components inside the projector are not sealed and therefore can become problematic with dust buildup.
On inorganic LCD projectors as well as DLP projectors, there is not a problem with image persistence. This is where an image may remain in organic LCD panels. It is easily erased, but is an issue that is often brought up by proponents of DLP projectors. DLP projectors never have image persistence problems. Image persistence is different than burn-in that old CRT monitors could suffer.
Image quality on a DLP chip does not degrade over time. It is possible that an LCD projector can lose some of its brightness and color brilliance with time. Manufacturers who make LCD projectors and have test data concerning the image degradation. However, they have not been eager to share their findings with the public. Image degradation is a non-issue with DLP projectors.
A few years ago another advantage that DLP projectors had over LCD was what was known as the screen door effect. This was where it was possible to see the individual pixels of an image projected through an LCD projector. With higher resolution projectors today, this is less of an issue. It is still a problem with low end, low resolution projectors, but is quickly disappearing. DLP projector manufacturers tout the fact that their product does not suffer from the screen door problem.
DLP Projector Disadvantages
The rainbow effect is a common problem with DLP projectors. This is where some people get a flash of color separation that occurs when there are moving images on the screen and the projector is rapidly changing colors through the spinning color wheel. This does not effect everyone. Some people may never see it and some people are sensitive to it. Those who readily see the rainbow effect find it distracting to watch a movie through a DLP projector. The effect can be eliminated for the vast majority of people by speeding up the rate in which the colors are changed per second. A 1x speed wheel (3600 RPM) showed the greatest problems with the rainbow effect. Most low-end DLP projectors today are 2x and those built for home theater use are 5x and 6x.
The edges of a projected image between dark and light colors are usually jagged. This is called dithering. This is how a image transitions from one color to another, or how a curve is rendered in an image. In DLP projectors the way this gray colored transition is represented is through switching the light on and off faster in that area. Sometimes it can cause a dithering artifact where one can see an inconsistency in the color transition.
Because of the nature of DLP technology, the amount of zoom achievable is restricted. There is also not as much flexibility in digitally enhancing lens shift. This means that a DLP projector is more restricted in where it can be installed. DLP projector owners will have fewer options when it comes to setting up a home theater. However, if the installation will be from a ceiling mount directly in line with the screen, then it is rarely a problem.
A final disadvantage to DLP projectors, and often brought up by LCD manufacturers, has to do with color brightness. While a DLP projector often has a higher contrast ratio they also suffer from unevenness in the brightness of the colors displayed. White and light colors will be stronger than darker colors. LCD projectors have the same amount of brightness across their images whether it is a bright or darker color.
DLP Projector Wrap-up
DLP projectors have many advantages over LCD projectors. Yet LCD technology is better in other areas as well. There is no easy answer as to which one is best overall. Choosing a digital projector, especially for a permanent installation, requires a lot of planning to know which technology to choose. Once the right technology is chosen, then there is a need to choose a specific projector. This information should help the purchaser make the right general choices.
Often the retailer that is selling a projector will have staff on hand to answer questions and guide the buyer into a right decision. This is true for online projector retailers as well as local projector stores. Don't hesitate to call for specific information from a projector dealer. They are usually glad to help.