Projector Display Technologies: DLP, LCD, LCOS

Intro

Continuing with our projector buying series, let’s delve into the different types of projectors and how they function. Our aim is to provide you with insights into their strengths and weaknesses, enabling you to not only understand the mechanics of each type, but to also help you make a more informed decision when shopping for a projector.

Display Technology

The term “display technology” refers to the method by which the projector generates images. It is not necessarily dependent on what produces the light (light source), but rather on how the projector manages and manipulates the light to produce the image displayed on the screen. While these display types can function with any of the mentioned light sources discussed at the end of the article, it is important to note that certain display technologies lend themselves more readily to integration with certain light source types.

Digital Light Processing (DLP)

DLP projectors utilize a Digital Micromirror Device (DMD) chip to reflect light and create images. This technology, born out of Texas Instruments’ innovation with DMD, operates by employing minuscule mirrors for each pixel. When integrated with a light source and a projection lens, each mirror on a DMD chip has the capability to tilt either toward or away from the light source, thereby controlling whether the corresponding pixel appears as on (light) or off (no light).

DLP projectors come in two main types: single-chip and three-chip models. Single-chip DLP projectors use a spinning color wheel that typically has the three primary colors, but it can also have the secondary colors as well. As this color wheel spins, it changes the color of the light that is reflected from the DMD chip. Because the mirrors on the DMD chip flip so rapidly they can create the red, green, and blue parts of the image multiple times per frame, and these colors blend together to form a complete image. However, because of the color wheel, the image might sometimes show rainbow artifacts, especially in your peripheral vision.

Example of a 1-chip DLP

Example of a 3-chip DLP

On the other hand, high-end models can use three separate DMD chips, each dedicated to one of the primary colors (red, green, and blue). The light source is split into each primary color, sent to its dedicated DMD, and then combined at the end to form a complete image. This configuration results in better brightness and a broader range of colors without the need for a color wheel, eliminating the issue of rainbow artifacts.

Advantages:

  • Generally lower cost compared to other technologies
  • Excellent ANSI contrast
  • Great sharpness
  • Excellent motion resolution
  • Good in brighter environments

Drawbacks:

  • Rainbow effect can make image unwatchable for some
  • Can have different brightness levels for color and white
  • Low On/Off Contrast compared to high-end 3LCD and LCoS
  • Limited dynamic range, so worse in dark content

DLP projectors are known for their sharpness and respectable ANSI contrast, making them an excellent choice for spaces with partial lighting. However, they may not preform as well in completely dark environments, as their limited dynamic range near black can cause dark scenes to appear somewhat gray and lacking in contrast.

The only exception to this are very high-end DLP models that are way beyond the consumer market, such as the Christie Eclipse, which uses 6 DMD chips to create virtually perfect black on screen – way surpassing even LCOS projectors for on/off contrast and then some. So we can conclude that DLP is suitable to create very high-end displays, if cost is no object. But not in the consumer market, where 4K DLP can only reach around 2000:1 on/off contrast with 4000:1 models not too far off on the horizon as technology improves. That will match high-end 3LCD units.

Liquid Crystal Display (LCD)

LCD projectors work by using three LCD chips to control brightness of the three primary colors: red, green, and blue. Unlike DLP projectors that are reflective in nature, LCD projectors are transmissive which makes their light path shorter and more compact.

The white light from the light source is divided into its primary colors—red, green, and blue—using special mirrors or prisms called dichroic mirrors. Each of these color beams is directed towards a separate part of the projector to be passed through its own LCD chip.

Inside each of the LCD chips, there are tiny liquid crystals for every pixel on the screen. By changing the electrical charge applied to these liquid crystals, the projector can control how bright each pixel is for each of the primary colors. This precise control ensures that each pixel displays the correct color and brightness needed to create the final image on the screen.

When an image or video is projected, the three LCD chips work together to regulate the intensity of each color, creating a full-color image. This image is then projected onto a screen or surface for viewing. Thanks to this precise control over brightness levels, the LCD panels in a 3LCD projector can create images with smooth transitions between different shades of brightness.

Advantages:

  • Excellent Color Volume
  • Equal white and color brightness
  • Better ANSI contrast than LCoS
  • Smaller LCD pixel size offers a distinctive advantage for pixel-shifting, with reduced overlap compared to DLP and LCoS
  • Possibility for great black levels for high-end units

Drawbacks:

  • Worse ANSI contrast than DLP
  • Elevated black floor is the same as DLP for lower-end units
  • Chicken wire effect: can see pixel grid up close, can be mitigated if projector is using pixel shifting technology

LCD projectors are renowned for their ability to deliver vivid and vibrant colors, mainly because they can produce color and white at the same brightness level—a distinction from single-chip DLP projectors that use “white boost”. Additionally, they are well-suited for pixel-shifting technologies, as their pixels do not overlap as much as those in DLP or LCoS machines. This advantageous feature often translates to cost savings when compared to full native resolution projectors. However, it is worth noting that LCD projectors still contend with challenges related to near-black contrast. Light leakage through the LCD panels can elevate the black floor, impacting the overall on/off contrast performance. To mitigate this, LCD projectors can use polarising filters to filter out unwanted light. This is what Epson uses in their Ultra Black (UB) range to essentially double the on/off contrast compared to the models without it, to around 4000:1.

Liquid Crystal on Silicon (LCoS)

LCoS projectors work by combining the technology from both DLP and LCD projectors. It was initially developed by multiple companies, but due to its complexity and cost only JVC (as D-ILA) and Sony (as SXDR) persisted in refining LCoS technology to a point where it became competitively priced and offered high performance. Historically, JVC’s LCoS projectors excelled in on/off contrast and proved to be more impactful in real-world content, while Sony’s led in ANSI contrast.

The way an LCoS projector works is as follows: The light source, whether it is a lamp or laser, goes through a lens to focus and direct the light. It is filtered to allow only visible spectrum light to pass through. The white light is then separated into discrete colored components using a light beam splitter or dichroic mirror. These colored beams are split into their primary colors: red, green, and blue, just like an LCD projector.

Credit: projectorscreen.com

Each of these primary colored beams is directed towards its designated LCoS panel. These panels consist of a liquid crystal layer sandwiched between a clear TFT (Thin-Film Transistor) and a silicon semiconductor. Before reaching the panel, these beams pass through polarizing filters and then interact with the chip. To put it simply, these panels work like a combination of an LCD chip and a DMD (Digital Micromirror Device) chip, with the LCD part regulating the intensity of each color of light, and the DMD-like section (the silicon chip/mirror portion) reflecting or deflecting the light to form the image.

Much like LCD projectors, LCoS technology adjusts liquid crystals within each pixel by altering electrical charges. This modulation enables pixels to go from complete black to fully transparent and all shades in between, allowing for a wide range of colors and gray levels. The modulated primary colored light, once it reflects from the silicon devices, passes through a prism to merge and form a full-color image. This completed image is then projected onto the screen through the projector’s lens.

Advantages:

  • Very high on/off contrast
  • Best black levels of display technologies in the consumer market
  • No rainbow or screen door effect
  • Most natural looking image
  • Better in low light environments
  • LCoS typically has a small inter-pixel gap, providing image stability and a film-like quality

Drawbacks:

  • Most expensive consumer technology due to chip complexity
  • Loses contrast advantage in non-light controlled rooms as ANSI contrast is comparable to other technologies
  • Typically not as bright as DLP or LCD projectors, although that is changing with laser-based models.

By using the reflective nature of the DLP process and the transmissive properties of the LCD process, the LCoS process can produce amazing on/off contrast, while keeping equal color and white brightness. It generally has a small inter-pixel gap making the image look more natural, but this can make the image look less sharp when compared to DLP and LCD projectors. Also, LCoS projectors tend to have a lower brightness due to the light having to pass through and reflect off of more surfaces when compared to the other technologies. However, the largest drawback to the LCoS projectors is the high cost due to its complex nature.

Light Sources

There are a few different types of light sources modern projectors use. Traditionally, lamp-based projectors were all that was available, but the improvements to LEDs and laser technologies have really started to take off in the projector market over the last while.

Traditional Bulb

Traditional projectors use bulbs as their light source, which require periodic replacements after a certain number of hours of use (3000-5000 hrs), adding to the total cost of ownership. While offering good performance, bulb-based projectors have drawbacks like the need for frequent lamp replacements, periodic maintenance, high heat generation, recalibration touch ups, and longer on/off times. These factors may result in increased cooling requirements, reduced component lifespan, and lower color gamut capability without the use of brightness robbing color filters.

Bulb projectors are a solid and reliable choice and they often do come in slightly cheaper upfront costs than LED or laser projectors, but be aware bulb projectors do come with the most maintenance out of the light source types.

LED

LED projectors utilize light-emitting diodes (LEDs) as the light source, offering advantages such as energy efficiency, longer lamp life (up to 20,000 hours or more), and quick startup times. They are more compact and produce less heat compared to traditional lamp-based projectors.

However, LED projectors may not achieve very high brightness levels like lamp-based projectors do for use on large screens or rooms with ambient light. They are also more expensive than lamp-based projectors and are best suited for use in light-controlled rooms due to their lower brightness capabilities.

Example of LED source in DLP projector

LED light sources are commonly found in lower-end projectors because they offer a cost-effective way to achieve a light source in a small package. However, there is a trade-off: LED lights are not as single-colored (monochromatic) as other light sources, which makes it challenging to achieve accurate color representation with them.

However, LED light source technology is still largely in the development stage and will improve over time, so it is very possible it will soon be a viable option for high end projectors.

Laser

Laser projectors use lasers as the light source, providing benefits like high brightness levels, wide color gamuts, and virtually maintenance-free operation without lamp replacements. They offer outstanding image quality and are suitable for both dark and well-lit environments. Laser-based projection is becoming the standard with extensive research and development invested. Laser projectors can use a single color laser or use 3 separate lasers for each of the primary colors (red, green, blue) for a wider color gamut up to BT.2020 without the need for color filters. They generate less heat, have near instant on/off times, and can deliver 20,000 or more hours of operation without a light source replacement.

Example of an RGB laser in a DLP projector

However, laser projectors tend to be the most expensive option among display technologies, particularly in the case of discrete RGB laser designs. They may exhibit the “laser speckle” effect, which requires internal filters or external screen vibrators for mitigation.

As it stands now, most laser light sources cannot be swapped out for a replacement. Once they reach the end of their life, the unit typically cannot be fixed. This is not usually a worry for most people because 20,000 hours of use translates to approximately 10 years if the projector runs for over 5 hours a day, and 18 years if run for only 3 hours. Lasers will keep working beyond this time, as this is only the time to half-brightness. It is likely that other components will fail in the projector before the light source does.

Which is Best?

When it comes to choosing the right projector technology and light source, it is all about aligning your preferences and needs. DLP projectors offer sharpness and low cost, but may struggle in very dark settings. LCD projectors excel in colors, but can also have contrast challenges unless you go for a high-end model from Epson. LCoS projectors have great on/off contrast and color accuracy, but come at a higher cost.

If you are worried about things like the rainbow effect in DLP projectors or laser speckle in laser projectors, it is a good idea to see them in action at a live demonstration. These issues may not become clear until you see them yourself, so experiencing them firsthand is essential for making an informed decision.

In my dedicated room, LCoS projection stands out as the most natural looking image for me. The significantly better on/off contrast and better black levels produce a more realistic image quality when compared to DLP and LCD. Regarding the light source, I lean towards laser projectors because they require less frequent calibration. Laser projectors can maintain their image quality over longer periods as their lasers degrade at a slower rate compared to bulbs. However, as of now, laser LCoS projectors cost a premium, but hopefully I will be able to make that jump within the next few years.

Projector Buying Guides:

Projector Buying Guide: The Room

Shopping for Projectors: Cutting Through the BS

What is Display Brightness, Contrast, Greyscale, Gamma and Colour?

Leave a Reply

Up ↑

%d