CARE OF PROJECTOR’S LAMP

Switching Projector On and Off

Each time you turn the unit on, there is an inrush current that applies stress to the lamp filament. The more often this stress is applied the sooner the lamp will fail. For this reason, turning the overhead projector "on" and "off" frequently during presentations is not recommended. Some projectors have a "soft start" power supply that provides a gradual voltage increase which limits the inrush current shock. This results in extended lamp life.

Cooling

Improper cooling can cause lamp envelope seal failure or lamp capsule swelling. Always make sure the fan is operating and the intake and exhaust vents are not blocked.

a lot of light the lamp generates a substantial amount of heat which must be transported away from the lamp because of risk of melting and exploding (the inside of the lamp is filled with an inert gas that’s excited with a high voltage generator to produce the light).

To get the excess heat away from the lamp and out of the projector one or more fans are used which generate the fan noise that projectors produce. Obviously small fans that turn at high rpms are more likely to be noisy than larger fans turning at moderate to slow rpms.

SPEED POWER ON/OFF FEATURE

most of the new models in the market are equiped with this "Speed Power On/Off " feature, whereby whenever this is applied, an inrush will be charged directly on the capacitor to activate the cooling system for the lamp .

However, in our experiece, we would advise you or the end-user of not having the habit to use this feature, better still not to use this feature at all, due to the following factors :

1) Frequent usage of the capacitor will reduces its lifespan and yet it does not have any indication of diminishing lifespan.

2) This projector as "High-Powered Projector" meant Heavy usage of prolong hours and high brightness==> requires sufficient cooling effect before power shut-down. and yet presuming that it is unknown that the capacitor's lifespan is over and not functioning, the user  will not exercise the normal way "proper shut-down", thus causing the lifespan of the lamp to be shorter and may even affect the panel board as well. We cannot deny such scenario may happen, so we still strongly advise that "Proper shutting of the projector" to be exercised at all time.

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Introduction to LCD / DLP Projectors

With the introduction of the LCD projector about a decade ago it was only a matter of time before high quality projectors would come down in price enough to make them affordable. As a result the long kept dream of many home theatre enthusiasts came a step closer, as buying a projector no longer meant you had to get a second mortgage on the house. The low price point of modern projectors, combined with their excellent display capabilities, makes them very suitable to have a true movie theatre experience at home.

In this article we’ll take a look at three entry level multimedia projectors, the Dell 2100/2200MP, the InFocus ScreenPlay 4800 and the Sanyo PLV-Z1, to see how they stack up to each other and what the price/performance level of these entry level devices is. We’ll also go over the technology used in these projectors and discuss why lumen output, contrast and resolution are important when choosing a suitable projector for use at home. Armed with that background information we’ll be better able to understand what makes these devices work and what to look for in a quality projector. So, without further ado, let’s take a look at some of the projector basics such as lumen output, contrast and more.

Lumen output

The amount of light projected at the screen by a projector is measured in ansi-lumen but we’ll simply call it the lumen output. The actual number listed in a projector’s spec sheet is about as meaningless as can be, as all it says is that a 2000-ansi-lumen projector has a higher lumen output than a 1000-ansi-lumen projector. It however doesn’t say anything about the quality of the image or whether a 2000-ansi-lumen projector is better than a 1000-ansi-lumen one. For every single projector the quality and the readability of the projected image depends on the amount of ambient light and the size of the image we’re projecting.

If we're for example projecting in a darkened room, the 2000-ansi-lumen projector won’t have an advantage as the 1000-ansi-lumen projector will have sufficient lumen output under these conditions to create a crisp and clear image. The reason why is simple, because there’s no, or not enough, ambient light to affect the projected image. The other way around the lumen output does matter however, if we’re for example projecting in a well lit room, for example a company board room, then more lumens will mean a better defined image, so the 1000-ansi-lumen projector is at a disadvantage here.

However we must not forget that in order to be able to make any comments about the readability and quality of the projected image we need to factor in the size of the projected image. If we, for example, take another look at the 2000-ansi-lumen projector and have it project an image of 2 x 1.5 meters and we enlarge the image size to 4 x 3 meters, then the surface area of the projected image has been multiplied by four and thus the brightness of the projected image is just a quarter of the original 2 x 1.5 meters image.

So, in a nutshell, the lumen output of a projector is important, but only if you factor in the lighting conditions of the room it’ll be used in and the size of the image that you’ll be projecting. In the case of a home theatre, lumen output isn’t really an important factor, as we’re always projecting in a darkened room and at a known image size. Most home theatre setups use a projector with a lumen output around 500 ansi-lumen to not saturate and reduce the contrast of the projected image.

Contrast

Contrast is a much more important factor to consider as the contrast ratio of a projector tells us how large the difference is between the projector projecting a black and a white image. Contrast is directly related to the readability of the projected image, whether we project in a darkened or well lit room and at any projected image size. Many LCD projectors have a contrast ratio of 400:1 which means that the lumen output of a projected white image is 400 times greater than that of a projected black image. A projector with a higher contrast ratio will always project a richer image with more better color saturation than a projector with a lower contrast ratio simply because the difference between black and white is greater.

For home theatre the contrast ratio is one of the most important factors because we project in a darkened room. If the projector does not have a sufficient contrast ratio the projector will seem to project black as a dark grey. When watching movies with lots of dark scenes details will fade away into the gray as the projector is unable to display sufficient contrast levels to bring out the fine details. So the contrast ratio of a projector is very important, the higher the better. A higher contrast ratio will always pay off, under any condition.

Resolution

All modern projectors have a resolution of at least SVGA, 800x600, which makes them perfectly suited for projecting video signals coming from TVs, VCRs and DVD players. Furthermore all modern projectors are capable of projecting higher resolution images, such as XGA, 1024x768, without a problem, as they downsample the image to the projector’s native resolution. Because most projectors feature a 4:3 resolution for widescreen video signals only part of the vertical resolution is used. For example when projecting a widescreen, 16:9, movie which has a 720x576 resolution only part of the 600 vertical pixels will be used to project the image, unlike the horizontal resolution where almost all pixels are used.

Projectors are naturally suited to project both interlaced and progressive scan signals. Interlaced signals are comprised of the image divided into even and uneven horizontal scanlines which are displayed one frame after the other, which means that after two frames the full image is formed. Progressive scan signals are generated by combining the two interlaced frames and only sending the full image, not the interlaced frames, which means that processing is needed to calculate the frames in between. Just keep in mind that the way a projector works the signal is always internally converted to a progressive scan signal. It is the quality of the internal processing which largely determines image quality with video playback and can make or break a projector' video playback.

Noise levels

The amount of noise the projector produces when switched on is another important factor to consider, especially in a home theatre setup. As a loud projector will be audible over the sounds from the movie you’re watching, which never is a good thing as that’ll draw your attention away from the movie you're watching. Naturally some projector noise is unavoidable as the lamp inside it needs to be properly cooled, thus you can’t simply do away with the fan noise.

Most home theatre projectors have a noise level of about 37dBA which makes them quiet enough for watching movies at a low to moderate sound volume without being distracted. The crux of the matter however is where the projector is located; if you place it right behind you it might still be loud enough to be distracting, so projector placement is very important here. And naturally not everybody thinks fan noise is distracting. Whether or not you find a projector’s noise level obtrusive is often a subjective matter which is different for each individual.

LCD, liquid crystal display

Basically there are two technologies commonly used in modern projectors and those are LCD and DLP. LCD, Liquid Crystal Display, is by far the oldest technology which has been developed decades ago and first debuted in wrist watches and more recently in flat panel monitors. The same technology is used in an LCD projector, although somewhat different than we’re grown accustomed to from, for example, flat panel monitors. In principle a LCD projector is not very different from a slide projector, with the slide being replaced by an LCD display. Modern LCD projectors use three LCDs, one for each primary color, red, green and blue. By making combinations of these colors a total of 16.7-million different colors can be generated.

If we look at the basic construction of a LCD projector we see a high-pressure gas-discharge lamp, a combination of mirrors and lenses and three LCD displays. The lamp obviously generates the light needed to project the image. Most lamps used in projectors have a 150-watt rating which means that 80 to 90% of the projector’s power consumption is due to the lamp. Besides a lot of light the lamp generates a substantial amount of heat which must be transported away from the lamp because of risk of melting and exploding (the inside of the lamp is filled with an inert gas that’s excited with a high voltage generator to produce the light). To get the excess heat away from the lamp and out of the projector one or more fans are used which generate the fan noise that projectors produce. Obviously small fans that turn at high rpms are more likely to be noisy than larger fans turning at moderate to slow rpms.

The LCD displays used in projectors are different than does we see in, for example, a flatpanel monitor, a notebook or a PDA. The LCD displays are manufactured using PolySi technology which gives them good resistance against high temperatures and excess doses of UV light from the lamp. Furthermore they feature a much higher contrast and resolution than normal LCD displays and are much smaller, with sizes up to about an inch measured diagonally. As mentioned three screens are used to form the image, each of which is only projecting one of the primary colors, green, red or blue. The colors are filtered out by mono- and dichromatic mirrors prior to entering the LCD displays. The images formed by the three LCD displays are then combined in a prism and projected to the screen through the projection lens.

The use of three LCD displays has a number of advantages; first off we’re now able to work with the three primary colors and can adjust the amount of red, green and blue in the final image as we please. If we’d have used a single color LCD, the color reproduction, brightness and the contrast would be fully accountable to that single LCD display, which will, in the end, result in a lesser quality image. A disadvantage of using three LCD displays is obviously that the images from all three LCDs must align perfectly at the screen to create a quality image. Another disadvantage of LCD technology is the rather low contrast which is limited by the amount of light still projecting through an LCD display when it is fully darkened. Another disadvantage is that every single pixel on the LCD display is surrounded by a small border, which will remain dark at all times. Upon looking closely at an image projected by an LCD projector we can see this effect, which is called the screendoor effect. It looks as if a fine grid is laid upon the image which can or cannot be clearly seen depending on the distance to the screen and the projected image size. Modern LCD projectors have about an 80% effective pixel area due to this effect.

DLP, digital light processing

DLP, Digital Light Processing, is a relative new technology that uses a digital mirror, composed of millions of small moveable mirrors, to project the image. Each mirror can either be switched on, and projects a ray of light through the lens, or off, which will not result in any light entering the lens. The actual image is formed on the mirror and reflected off of it through the projection lens onto the screen. Color is added in a DLP projector by using a rotating color wheel with the three primary colors, red, blue and green, in front of the mirror and then combining the images for these three colors faster than the human eye can see. Obviously with these three primary colors every possible color can be displayed, simply by switching the mirrors on and off at a higher or lower frequency in synchronization with the color wheel. A brighter red simply means that during the time that the red segment of the color wheel is in front of the mirror, the mirrors are more on than off and more of the red light is projected through the lens.

The basic construction of a DLP projector isn’t that different from a LCD projector, with the biggest difference being the fact that we’re projecting onto a mirror instead of through a number of LCD displays. Again we see the use of a high pressure gas-discharge lamp as a light source. The light from the lamp shines through the rotating color wheel and the colored light is then projected onto the digital mirror and the image on the mirror is synchronized with the color wheel so the image is displayed properly. One of the advantages of using a rotating colorwheel is that often also a transparent segment is used which greatly enhances contrast, as white light is not created by combining the three primary colors, but by simply synchronizing the transparent segment. A downside of using the colorwheel obviously is the fact that not all colors can be displayed simultaneously; only one color can be displayed at any given time. That also is a disadvantage of a DLP projector as the rapid switching between colors cause for some people to see ‘rainbows’ across white text or white objects in movies. This is simply caused by the rotation of the colorwheel and may, or may not, be noticeable. During our testing we found that these effects wear off over time if we even noticed them.

A well documented advantage of a DLP projector is a reduction of the screendoor effect, about 90% of the surface area of each mirror is used for projecting the image, and thus the effective pixel area is much larger. Another advantage is the high contrast ratio; most DLP projectors have a 2000:1 contrast ratio, which is much higher than most LCD projectors which, on average, have a 500:1 contrast ratio. The projected image therefore has blacker blacks and whiter whites in comparison to an LCD projector. Another optical advantage is the fact that the path the light has to travel in the projector is much shorter in a DLP projector. A DLP projector is pretty straightforward and the only object in between the image on the digital mirror and the projection screen is the projector’ lens. This obviously has a positive effect on color balance and reproduction as well as being a more elegant solution overall.