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Projector LCD/DLP - Glossary and the technology

1 .  Why use a projector?
2 .  Criteria for selecting a Data Projector
3 .  Brightness and Contrast
4 .  Resolution
5 .  Controls
6 .  Portability
7 .  Cost
8 .  LCD/Polysilicon Technology
9 .  DLP Digital Light Processing
10. Rebadging
11. Metal Halide
12. The Future
13. Data Projectors vs CRT Projectors
14. Plasma Displays
15. Rainbow Effect

1. Data Projectors
The days of using a box of overhead foils and a few coloured marker pens have long since gone for making serious business presentations. Static presentations from ohp or 35mm slide now look old fashioned and offer no opportunity to make last minute changes.

PowerPoint presentations incorporating your company logo, animation and perhaps some sound are now the norm. With perhaps 2 or 3 people a normal computer screen may suffice, but with groups of 6 or more people some means of showing a larger image is required - hence the data projector.

Data projectors are self-contained units containing their own lcd panels, light source and lens in one compact unit. They work with PC and Mac computers duplicating the image being shown on the monitor without any need for special software or complex setting up.
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2. Criteria for selecting a Data Projector

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3.   Brightness and Contrast
All manufacturers are fighting to increase the brightness of the projected image. Brightness is measured in terms of 'ANSI lumens' and the brightest machines command a premium price. Projectors in the range 300-600 lumens are best used away from direct daylight and with no office lighting. Units in the range 600-1,000 lumens can be used in most office condition away from direct sunlight. Units above 1,200 lumens are ideal for larger offices and conference rooms. No projector can really compete against direct sunlight!

Contrast attracts less attention but is important. Contrast measures the difference in light intensity between the dark and light areas of the screen. A high contrast figure is best; typically data projectors work in the range 150 to 400. DLP technology units tend to produce a higher contrast image.
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4.   Resolution
The sharpness and clarity of the image is determined by display resolution. The resolution of a display is given in terms of columns and rows of pixels making up the picture.

SVGA or 'Super VGA' resolution is most popular in schools and churches and features 800 columns by 600 rows. Whilst not essential it is a good idea to match the native resolution of the projector to that of the computer used to drive it.

XGA (1024 x 768) is becoming increasingly popular for business use as this is also becoming the norm for newly introduced laptops. There has also been a significant reduction in the price of XGA projectors. These units give a sharper image and are valuable for projecting more detailed images, smaller text etc.

Higher resolution SXGA units are available but in the main are reserved for specialist applications.
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5.   Controls
Normally there are a set of controls on the projector itself, with most being duplicated on an infra-red handheld remote. The controls would normally allow adjustment of brightness, contrast, colour tint, source (data or video), volume and image orientation. Zoom and focus controls can be controlled in a similar fashion or they may be manually adjusted using rings on the front of the projector.

In addition to controlling the projector, most handheld remotes are designed to control the computer by simulating the actions of the mouse. This is particularly useful when moving through a PowerPoint presentation a slide at a time. Using the remote mouse to navigate the more detailed menu operations can be cumbersome and it may be best to resort back to the keyboard!
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6.   Portability
Projectors are often considered as being in one of three categories: Personal, Conference Room, and Fixed.

Personal Projectors. In the same way as computers became more personal with the laptop, the reduction in price and size of projectors means that mobile presenters are owning their own projector rather than it being an office commodity. Typically a personal projector will be below 4kg and such that it can be carried as hand luggage on a plane.
In driving down the size of these projectors there can often be a price to be paid. New smaller projectors can attract a premium price, they can often be noisy, bulb life can be less, the speakers are smaller, the number of features may be less.

Conference Room Projectors. Ideal for use within the office and occasional movement by car. They are often used as a central resource by executives within the company. Typically they will weigh between 5 and 8kg. They would be expected to have a brighter, longer lasting bulb, a more extensive zoom control, stereo sound through larger speakers, dual data plus video inputs and quieter operation.

Fixed Projectors. These units are fixed installations within the conference room. They are the modern alternative to the 3 gun CRT projectors of old. Their capital costs and also the running costs are significantly less than the CRT alternative. A brightness of 2,000+ lumens would be expected.
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7.   Cost
Budget low powered projectors are in the range 1,000 to 2,000. These units are often used within a company's in-house training facility where low levels of light can be guaranteed.
Most portable SVGA units are in the range 1,500 to 2,000.
Machines above 2,000 are XGA units with a brightness of 700+ lumens and are now used by most commercial organisations.

Some companies acquire their own projectors whilst others prefer to hire units when required. Where a projector is only going to be used 3 or 4 times a year, them hiring makes good sense. Similarly where a unit is going to be used once or more every month, then purchasing can be justified. The break point between hire and purchase is somewhere in the region of 7 hires per year.
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8.   LCD/Polysilicon Technology
LCD (Liquid Crystal Display) is the established technology. Electrical signals turn on individual pixels in a matrix of cells. Normally there are three sets of panels, one for each of the three primary colours, red, green and blue. LCD technology produces rich saturated colours that are well suited to business presentations.
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9.   DLP Digital Light Processing
DLP (Digital Light Processing) is a newer technology that has been developed by Texas Instruments. There is a single chip that has on the surface an array of tiny aluminium mirrors, each of which represents a single pixel on the screen. Each mirror is hinged and is controlled by its own cell beneath it. The mirrors tilt to deflect the light from the lamp or reflect it through the lens onto the screen as a single pixel. Amazingly there can be over 1 million mirrors on a single chip that is about the size of a thumb nail!

DLP images may produce truer colours than LCD but the colours are not as vivid or as saturated. A DLP image is smoother and less pixelated than LCD and is well suited to displaying video images, the images tend to have a higher contrast than LCD produced images. This is a new technology and it is unclear as whether or not it will displace LCD technology.
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10. Rebadging
There are approximately 30 companies manufacturing data projectors, but there are over 60 brands of machines available. It is therefore inevitable that the same machine from the same factory is found on the market carrying different labels. For example Boxlight products are virtually identical to the InFocus machines. PLUS machines have been badged by the likes of Sharp and NEC. This is not necessarily a bad thing - if you look around you can often find the same machine under a different badge at a lower price.
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11. Metal Halide
Conventional bulbs use a metal filament that glows hot to produce light. Metal halide bulbs discharge electricity through a gas to produce an intense white light. Metal halide is used in all but the budget range of projectors. The bulbs are expensive (£200 - £400), but fortunately they are expected to last for 1,000 hours or more - significantly longer than a more conventional filament bulb.

If a metal halide bulb is turned On or Off too frequently the life of the bulb will be reduced. Similarly when turning off the projector it is often advisable to switch off the bulb whilst leaving the power on for a couple of minutes to allow the fans time to cool down the bulb. Most projectors will display the number of hours that the bulb has been in use, once this reaches 50% of the rated time it would be a good idea to purchase a spare bulb.

Metal halide bulbs glow less bright with time, if you feel that the image is not as bright as it once was, it may time to consider renewing the bulb.
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12. The Future
Projectors will continue to get brighter and smaller. The resolution of projectors will increase in line with the resolution of the laptops that are being used to drive them. In some applications it may be that projectors will be displaced by flat Plasma displays.
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13. Data Projectors vs CRT Projectors
CRT projectors are the '3 gun' units that are seen installed in the larger conference and lecture rooms. They can be used to project video/TV images as well as data from a computer. They are particularly suited to video/TV as the units can be 'tuned' to handle a wide range of signals. CRT units are expensive to buy, difficult to install and require trained technicians to set them up.

With the rapid development in LCD/DLP data projectors, CRT units are being used less and less as they cannot compete on cost, brightness or portability.
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14. Plasma Displays
The 42" (diagonal) plasma displays from the likes of Panasonic, Philips and Fujitsu are becoming increasingly popular. They have a number of benefits including:

The display consists of a thin layer of gas between two thin glass plates, each of which is covered by a matrix of electrodes. Applying a voltage across a pair of electrodes causes a single pixel to emit light. Precise image control is obtained without the depth requirements of the conventional CRT tube.
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15. Rainbow Effect
Rainbow effect other wise known as colour separation is caused as the result of the spinning colour wheel used in single chip DLP based projectors. In conventional 3x LCD panel projectors the image and colour are created by the LCD panels (R,G,B) . In single chip DLP projectors the image is created by one DMD (Digital Mirror Device) and the colour is added by shinning the reflected light through a spinning multi segment colour wheel. By using DLP Technology, projectors can be made lighter in weigh and smaller in design while also producing contrast ratio's of up to 2000:1 and beyond

Rainbow effect can be seen in varying degrees from person to person and from projector to projector and manifests itself by the appearance of a coloured shimmer on the following edge of moving images, partially in high contrasting scenes.
To overcome this minor problem some manufacturers have developed faster spinning and more segmented colour wheels.
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