Laser Video Projectors - What You Need To Know

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Let There Be Light!

Epson Dual Laser with Phosphor Video Projector Light Engine
Epson Dual Laser with Phosphor Video Projector Light Engine. Image provided by Epson

Video projectors bring the movie-going experience home with the ability to display images that are much larger than most TVs can provide. However, in order for a video projector to perform at its best, it has to provide an image that is both bright and displays an extensive color range.

To accomplish this task, a powerful built-in light source in needed. Over the past several decades, different light source technologies have been employed, with Laser being the latest to enter the arena.

Let's take a look at the evolution of light source tech used in video projectors and how Lasers are changing the game.

02
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The Evolution from CRTs to Lamps

Video Projectors - CRT (top) vs Lamp (bottom)
Video Projectors - CRT (top) vs Lamp (bottom). Images provided by Sim2 and Benq

In the beginning, video projectors (and rear projection TVs) employed CRT technology (think very small TV picture tubes). In this system, three tubes supplied both the needed light and image detail in either red, green, or blue form.

Each tube projected onto a screen independently. In order to display an image with the full range of colors, the three tubes had be converged. This meant that the color mixing actually took place right on the screen and not inside the projector.

The problem with using tubes, was the need for them to be periodically aligned/converged to preserve the integrity of the projected image, and if one tube faded or failed prematurely, all three tubes had to be replaced so that they were at the same starting point.

Also, the tubes ran very hot and needed to be cooled by special "gels" or "liquid". To top it off, both CRT projectors and projection TVs consumed a lot of power.

Functional CRT-based projectors are now very rare. Tubes have since been replaced with lamps, combined with special mirrors or color wheel that separates the light into red, green, and blue, and a separate "imaging chip" that provides the image detail.

Depending on the type of imaging chip used (LCD, LCOS, DLP), the light coming from the lamp, mirrors, or color wheel, either passes-through, or reflects-off of the imaging chip, which produces the picture you see on the screen.

The Problem With Lamps

LCD/LCOS and DLP "lamp-with-chip" projectors are big leap from their CRT-based predecessors, especially in the amount of light they can put out. However, lamps still waste a lot of energy outputting the entire light spectrum, even though only the primary colors of red, green, and blue are actually needed from the light source.

Although not as bad as the CRT option, lamps still consume a lot of power and generate heat along the way, necessitating the use of a potentially noisy fan to keep it cool.

Another issue is that from the first time you turn on a video projector, the lamp starts to fade and will eventually be too dim or burn out (usually after 3,000 to 5,000 hours). Even CRT projection tubes, as big and cumbersome as they were, lasted a lot longer. The short lifespan of lamps necessitates the added cost of periodic replacement. Add today's demand for eco-friendly products (many projector lamps also contain Mercury), there is a need for an alternative that can do the job better.

03
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LED to the Rescue?

Video Projector LED Light Source - Generic Example
Video Projector LED Light Source Generic Example. Image courtesy of NEC

One alternative to lamps: LEDs (Light Emitting Diodes). LEDs are much smaller than a lamp, and can be assigned to emit just one color. This enables them to emit red, green, or blue light.

With their smaller size, very compact sized projectors are possible—even inside something as small as a smartphone. Also, LEDs are more efficient than lamps, but they still have a couple of weaknesses.

First, LEDs are not as bright as lamps (when you compare an LED vs lamp projector in same price range).

Second, LEDs do not emit light coherently. This means is that as the light beams leave an LED chip-based light source, they have a tendency to slightly scatter, meaning that, although they are more precise than a lamp, they are still slightly inefficient.

One example of a video projector that employs LEDs for its light source is the LG PF1500.

04
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Enter The Laser

Mitsubishi LaserVue DLP Rear-Projection TV Example
Mitsubishi LaserVue DLP Rear-Projection TV Example. Image provided by Mitsubishi

To solve the problems of lamps or LEDs, a Laser light source can be used.

Laser is an acronym for Light Amplification by Stimulated Emission of Radiation.

That sounds pretty scary. When we think of lasers, what usually comes to mind are deadly military weapons (thanks, Sci-Fi movies). Although Lasers do have an increasing role in the military (such as in missile and bomb guidance systems)—the dreaded fully-realized "death ray" isn't quite there yet.

Lasers have been in use since about 1960 and most uses are more benign. They are widely used as tools in medical surgery (such as LASIK), and in education and business in the form of laser pointers and distance surveying. Also, if you own a Laserdisc, DVD, Blu-ray, Ultra HD Blu-ray, or CD player, lasers are used to read pits on a disc that contains music or video content.

The Laser Meets The Video Projector

When used as a video projector light source, Lasers provide several advantages over lamps and LEDs.

  • Lasers solve the light scattering problem by emitting light coherently. As the light exits the laser it remains as single tight beam, whose "thickness" is retained over distance unless changed by passing through additional lenses.
  • Lower Power Consumption. Due to the need to provide enough light for the projector to display an image on screen that may be several feet away, a lamp consumes a lot of power. However, since each Laser only needs to produce one color (similar to an LED), it is more efficient, resulting in less power consumption.
  • Increased Light Output with less heat generation—especially important for HDR, which requires high brightness for full effect.
  • Provides support for wider color gamut and more precise color saturation.
  • Virtually Instant On/Off time—more like what you experience when turning a TV on and off.
  • Longer useful source life—20,000 use hours or more is easily attainable. This capability eliminates the need for periodic lamp replacement.

The Mitsubishi LaserVue

Mitsubishi was the first to use lasers in a consumer video projector-based product. In 2008, they introduced the LaserVue rear-projection TV. The LaserVue used a DLP-based projection system in combination with a laser light source. Unfortunately, Mitsubishi discontinued all their rear-projection TVs (including the LaserVue) in late 2012.

The LaserVue TV employed three lasers, one each for red, green, and blue. The three colored light beams were then reflected of a DLP DMD chip, which contained the image detail. The resultant images were then displayed on the screen.

Having seen a LaserVue TV in operation, the results were pretty impressive. Excellent light output capability, color accuracy, and contrast. On the other hand, LaserVue sets were very expensive (65-inch set was priced at $7,000) and although slimmer than most rear projection TVs, was still bulkier than Plasma and LCD TVs available at the time.

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Video Projector Laser Light Source Configuration Examples

DLP Laser Video Projector Light Engines - RGB (left), Laser/Phosphor (right) - Generic Examples
DLP Laser Video Projector Light Engines - RGB (left), Laser/Phosphor (right) - Generic Examples. Images courtesy of NEC

NOTE: The above images and following descriptions are generic in nature—there may be slight variations depending on manufacturer or application.

Although LaserVue TVs are no longer available, Lasers have been adapted for use as a light source for traditional video projectors in several configurations.

RGB Laser (DLP)—This configuration is similar to that used in the Mitsubishi LaserVue TV. There are 3 lasers, one that emits red light, one green, and one blue. The red, green, and blue light goes through a despeckler, a narrow "light pipe" and lens/prism/DMD Chip assembly, and out of the projector onto a screen.

RGB Laser (LCD/LCOS)—Just as with DLP, there are 3 lasers, except that instead reflecting off DMD chips, the three RGB light beams are either passed through three LCD Chips or reflected off 3 LCOS chips (each chip is assigned to red, green, and blue) to produce the image.

Although the 3 laser system is currently used in some commercial cinema projectors, due to its cost, is not currently used in consumer-based DLP or LCD/LCOS projectors—but there is another, lower cost, alternative that is becoming popular for use in both types of projectors—the Laser/Phosphor system.

Laser/Phosphor (DLP)—This system is a little more complicated in terms of required number of lenses and mirrors needed to project a completed image, but by reducing the number of Lasers from 3 down to 1, cost of implementation is greatly reduced.

In this system, a single Laser emits blue light. The blue light is then split in two. One beam portion continues through the rest of the DLP light engine, while the other beam strikes a rotating wheel that contains green and yellow phosphors, which, in turn, create two green and yellow light beams. These added light beams, then join the untouched blue light beam, and all three pass through the main DLP color wheel, a lens/prism assembly, and reflected off the DMD chip, which adds the image information to the color mix. The result is a complete color image that is sent out from the projector to a screen.

One example of a DLP projector that employs the Laser/Phosphor option is the Viewsonic LS820.

Laser/Phosphor (LCD/LCOS)—For LCD/LCOS projectors, incorporating a Laser/Phosphor light system is similar to that of DLP projectors, except that instead of using a DLP DMD chip/Color Wheel assembly, the light is either passed through 3 LCD or reflected off of 3 LCOS chips (one each for red, green, and blue).

However, Epson employs a variation employs 2 lasers, both of which emit blue light. As the blue light from one laser passes through the rest of the light engine, the blue light from the other Laser strikes a yellow phosphor wheel, which, in turn, splits the blue light beam into red and green light beams. The newly created red and green light beams then join up with the still intact blue beam and pass through the rest of the light engine.

One Epson projector that uses Dual Laser in combination in a LCD projector is the LS10500.

Laser/LED Hybrid (DLP)—Still another variation, that is used primarily by Casio in some of their DLP projectors, is the Laser/LED hybrid light engine.

In this configuration, an LED produces the needed red light, while a Laser is used to produce blue light. A portion of the blue light beam is then split off into green after striking a phosphor color wheel.

The red, green, and blue light beams then pass through a condenser lens and reflect off of a DLP DMD chip, completing the image creation, which is then projected to a screen.

One example of a Casio projector with a Laser/LED Hybrid Light Engine is the XJ-F210WN.

06
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The Bottom Line - To Laser Or Not To Laser

BenQ Blue Core LU9715 Laser Video Projector
BenQ Blue Core LU9715 Laser Video Projector. Image provided by BenQ

The Laser option provides the best combination of needed light, color preciseness, and energy efficiency for both cinema and home theater applications.

Although projectors with lamps still dominate home theater projector offerings, use of LED, LED/Laser, or Laser light sources are increasing. Laser is currently used in a limited number of high-end video projectors, so they will be the most expensive (official prices typically start at about $3,000—also consider the cost of a screen, and in some cases, lenses).

However, as implementation increases and consumers buy more units, production costs will come down, resulting in lower priced Laser Projectors that will be competitive with the lamp based option (also take into consideration that cost of replacing lamps vs not having to replace lasers)

When choosing a video projector—no matter what type of light source it uses, needs to fit your room viewing environment, your budget, and most of all, the images it projects need to be pleasing to you.

Before deciding if a video projector using a lamp, LED, Laser, or LED/Laser hybrid is the best  option for you, seek out a demonstration of each type.

For details on what to consider in terms of video projector light output, as well as how to set up a video projector, refer to our companion articles: Nits, Lumens, and Brightness - TVs vs Video Projectors and How To Set Up A Video Projector

One last point—Just as with "LED TV", the laser(s) in a projector don't produce the actual detail in the image, but provide the light source support that enables projectors to display full color-range images on a screen at sufficient brightness. However, it is easier just to use the term "Laser Projector" rather than "DLP or LCD video projector with a Laser Light Source".