Technology

DLP

DLP projectors come in single or 3 chip models, the latter currently the exclusive domain of very high end units. Due to cost considerations, the majority of DLP projectors will be single chip.

DLP is a digital reflective technology. A DLP panel is made up of 'Digital Micro-Mirror Devices' (DMD), this consists of thousands of tiny mirrors each individually hinged designed to reflect a single pixel, therefore a true HD panel will have 1920 x 1080 individual mirrors (2,073,600 in total). Each individual mirror can be switched on or off (moved up or down) several thousand times per second.

The integral colour wheel filters the light into red, green and blue, from which a single chip system can create 16.7million colours and the 3 chip found in high end units can produce 35 trillion colours. As each mirror will be less than one fifth of the thickness of a human hair and the mirror will be spaced less than one micron apart, this creates what will appear to be a smooth image without window-box effect.  This, when combined with the fact that the image is reflected and not having to pass through the chip means that a DLP chip is often specified for video applications due to its vastly superior contract ratio.

A DLP unit is sealed which prevents contamination from dust particles and as such will not require a filter system, this can often lead to lower maintenance costs.

• Sealed Units
  No need for filters and the associated maintenance of cleaning and changing. 24/7 operation. DLP projectors can be run continually for long periods of time without large scale image degradation. Many vendors will therefore offer 24/7 warranties.
• Seamless Image
  As the 'digital micro devices' are less than one micron apart the image appears seamless, in part for this reason many people consider that DLP can be better for video applications.
• Colour Consistency
  On high end projection where edge blending is required many technicians consider that the consistency of colour between projectors is more equal than on many LCD units, this often makes blending easier and more reliable.

See DLP Technology

LCD

LCD projectors contain three panels one each for green, blue and red, each panel consisting of a layer of liquid crystal. Unlike the DLP panel the LCD is Tranmissive in that the light is shone through the panel. Each individual panel consists of a grid work of smaller squares each representing one pixel in the final image. The panels work by an electrical charge being applied to them, causing the crystals to rotate the plane of polarised light, which effectively turns the individual colours on or off. As the resultant polarised light comes out of the panels it passes via a prism which forms the projected image.

There are many factors that can affect the quality of the image; LCD panels come in various sizes, typically from sub 1 inch to 1.8 inch on the larger brighter projectors. Recent developments include in-organic panels which have a thinner grid work within them, allowing more light to pass through and also reducing the 'chicken wire' grid effect that can often appear if you look very closely on a white or pale image. LCD projectors can often be more cost effective than DLP and as a result LCD panels are often used in higher lumens unit, as they provide a more cost effective solution.

• Inorganic Panels
  Whilst most LCD projector warranties do not cover the unit if it is used continually for more than 8 hours, some vendors are introducing inorganic panels and are now removing time limits from warranties.
• Lower Cost
  LCD is a longer established technology and whilst DLP prices have been falling LCD often still has a price advantage, this is most notable on higher end projectors, especially over 7000 lumens.
• Filters
  LCD units are not sealed and therefore need filters to prevent damage from dust particles, however great effort has been made in recent times to improve filter technology and increase times between changes. Several vendors on higher and mid end units are now introducing continual moving filter systems, some with a life span in the region of several thousand hours.
• Sharp images
  LCD produces a sharp image, this can be a disadvantage on video but on data applications it is ideal. As a result power point and complex graphs can often appear better on an LCD projector.

LCOS

LCOS is one of the newer projector technologies - a hybrid technology in which the light is reflected off modified LCD panels to offer some of the benefits of DLP, particularly at higher contrast levels and a higher "perceived" resolution because of the smoothness of the image.

LCOS consists of a layer of liquid crystal which sits on top of a pixelated, highly reflective substrate. Below this layer is another that contains the electronics that activate the pixels. Because the image is reflected off the substrate you do not get the cross hatching that is often found on a LCD projector, making a more seamless image than you would tend to get from a standard LCD. LCOS currently tends to be used more in the higher end resolution projectors such as SXGA+ and 1080p.

Features and Benefits of Lcos
LCOS tends to have a perception of excellent colour reproduction combined with high contrast ratios. It avoids the rainbow effect that can occur with DLP, however, currently it is limited to higher end units although this is expected to change rapidly as the technology falls in price.

LED

LED or Light Emitting Diodes refers to the method of creating the light used by the projector. There have been several less than successful attempts to produce LED projectors over the last few years, however very rapid advances over the last 18 months suggest that widely available and effective units are appearing now. They are expected to make a huge impact.

We are most familiar with LED technology from small bright torches that are appearing with increasing frequency. These have what appear to be several small bulbs (these are the diodes) as opposed to one larger bulb.

There are many advantages with LED, they use a very small amount of energy relative to the brightness produced, therefore there is a distinct possibility of battery operated portable projectors appearing on the market soon. Because of the reduced energy, mains operated units should be relatively cheap to run compared to many other alternative units. Finally the LED units do not produce much heat, this could have a considerable effect on the future design of projectors, less heat could lead to fan-less units and also have an effect on the design and use of filters .