• Learn About Rear Projection Televisions

    Learn About Rear Projection Televisions

    How do they work? What are the advantages and disadvantages of ownership? Is a rear projection television right for me?

    In this section we will demystify the technologies of the rear projection television.

    How Does It Work?

    The first thing to understand about rear projection televisions is that they use one of four technologies: CRT, LCD, DLP™ or LCoS. The various technologies that can be used inside a rear projection television are covered in depth in the Learn About The Technologiessection.

    Regardless of which technology powers a rear projection television, they all operate in much the same manner. All rear projection televisions start with a projector at the base of the television cabinet. This projector is simply a lower powered version of a front projector with a very short throw lens, meaning that its lens can make a very large image without having to be very far away from the screen.

    The projector is situated so its projected image is bounced off of one-to-two mirrors, depending on which technology is used. CRT-based rear projection usually uses one mirror, while microdisplay technologies use two. The image is then projected onto a special screen that allows it to be seen through the screen, which is called a rear projection screen. Figure 1. shows a typical set up for a microdisplay (DLP™, LCD, or LCoS) powered rear projection television, and a CRT powered rear projection television.

    Learn About Rear Projection Televisions

    Pros and Cons

    In this section, we will break down each technology to give you a more accurate picture of the advantages and disadvantages that each type of rear projection television presents.

    CRT-Based Rear Projection Televisions

    Pros:

    1. Least expensive per diagonal screen size of all RPTV technologies.
    2. Color reproduction is excellent.
    3. Best absolute black levels available.
    4. Best contrast ratios available.

    Cons:

    1. They are large and heavy. You must have an enormous area available for them.
    2. Because they use three different CRT tubes, one each for red, green and blue, they need to be periodically converged. (See CRT Technology in our Learn About the Technologies section).
    3. They are a phosphor-based technology, which means that burn-in of an image can occur and that the display’s image quality will diminish with time.
    4. Not nearly as bright as microdisplay-powered rear projection televisions.
    5. Usually have very limited viewing angles. You must sit directly in front of the television to get a viewable image.
    6. The technology is being phased out.

    LCD (Microdisplay) Based Rear Projection Televisions

    Pros:

    1. Good color reproduction.
    2. Can be much slimmer and lighter than CRT-based rear projection televisions, enabling them to be placed where CRT-powered machines cannot.
    3. Although more expensive per viewing area than CRT based machines, they are still much less expensive than similar sized and resolution plasma displays.
    4. Very bright compared to the older CRT-based machines.
    5. All machines are at least at an HDTV resolution.
    6. Microdisplay technologies are easy to repair on-sight.
    7. Microdisplay technologies don’t suffer from burn-in.
    8. Better viewing angles than CRT-based rear projection televisions.

    Cons:

    1. Poor fill ratio enables the grid structure to be seen from relatively close up (aka the screen door effect).
    2. Dead pixels can, and usually do, happen.
    3. Improper convergence of three LCD panels can cause color to be off.
    4. Poor absolute black levels and shadow detail.
    5. Poor overall contrast ratios when compared to other microdisplay technologies.
    6. Not as slim as the newest DLP™ powered rear projection televisions.
    7. Lamp-based technology. Lamps must be replaced after 6-8,000 hours. Lamps are costly.

    LCoS (Microdisplay) Based Rear Projection Televisions

    Pros:

    1. Good color reproduction.
    2. Very high are resolutions available (true 1080p).
    3. Very high fill ratio gives smooth, film-like images
    4. Very bright when compared to the older CRT-based machines.
    5. Can be much slimmer and lighter than CRT-based rear projection televisions, enabling them to be placed where CRT powered machines cannot.
    6. Microdisplay technologies are easy to repair on-site.
    7. Microdisplay technologies don’t suffer from burn-in.
    8. Have better viewing angles than CRT-based rear projection televisions.

    Cons:

    1. Dead pixels can, and usually do, happen and because the technology is partially reflective, they can be more noticeable than on other technologies.
    2. Improper convergence of three LCD panels can cause the color to be off.
    3. Absolute black levels and shadow details are not as good as those on DLP™ powered rear projection televisions.
    4. Not as slim as the newest DLP™ powered rear projection televisions.
    5. Very expensive when compared to all other rear projection television technologies
    6. Yield rate is very low for LCoS machines and image quality can vary greatly from machine to machine.
    7. Lamp-based technology. Lamps must be replaced after 6,000-8,000 hours. Lamps are costly.

    DLP™ (Microdisplay) Based Rear Projection Televisions

    Pros:

    1. Good color reproduction.
    2. Can be very slim. New technologies are being introduced that allow some DLP™ rear projection televisions to rival plasma displays in depth. The new ultra-thin DLP™ displays can even be hung on walls.
    3. Although more expensive per viewing area than CRT-based machines, they are still much less expensive than similar sized and resolution plasma displays.
    4. Very bright when compared to the older CRT-based machines.
    5. All machines are at least of HDTV resolution.
    6. Best contrast ratio, absolute black levels, and shadow detail among the microdisplay technologies.
    7. Microdisplay technologies are easy to repair on-site.
    8. Microdisplay technologies don’t suffer from burn-in.
    9. Better viewing angles than with CRT-based rear projection televisions.
    10. No convergence issues.
    11. The only technology that is not organically-based. Image quality will not fade with time.
    12. Dead pixels are rare.

    Cons:

    1. Some people can detect the color separation issues, commonly referred to as the “rainbow” effect.
    2. Still bulkier than plasma or LCD displays.
    3. Lamp-based technology. Lamps must be replaced after 6,000-8,000 hours. Lamps are costly.

    Is a Rear Screen Right for Me?

    Is a rear projection television (RPTV) right for me? It depends on your needs. Rear projection televisions can be used in a broad range of applications, and it’s actually rare to find specific applications where one cannot be used. Below is a list of common scenarios where a rear projection television performs best, followed by a list of scenarios that might suggest the need to use a different technology.

    Best case scenarios:

    1. Applications where a large screen is desired and there is enough available floor area to place the unit.
    2. Installations that have custom cabinets that are designed for rear projection televisions.
    3. Applications that have budget constraints.
    4. Areas that have too much ambient light for front projection displays.
    5. Playrooms, bars, basements and all areas where the sole function of the room is not home theater. (Rooms like this are commonly referred to as media rooms).

    Scenarios where another technology might be more effective:

    1. Any in-wall application.
    2. Large rooms with controlled lighting.
  • Setting Up a Room for Front Projection

    So you have a room that you want to put a projection system in and it is time to start thinking about how it’s going to fit into the room. Where do you start?

    Step 1. How high is your ceiling?

    This may seem like a strange place to start, but your ceiling height controls screen height, which controls screen width, which controls how far back your projector must go, and ultimately, how far back you’ll need to place the seating in the room. Here’s why.

    Any screen you put into your home theater really should start at least three feet off of the floor. This will allow the audience to be looking up slightly — like in a real theater – and will contend with any potential visual obstructions such as a coffee table.

    Setting Up a Room for Front Projection

    Next, take your ceiling height, subtract three (3) feet from it and you’ll have your maximum screen height. This height might be larger than what you want, but it will give you an idea of how big of a screen will fit.

    Step 2. What aspect ratio screen do you want?

    After you find out the maximum height of your screen area, it is time to figure out the maximum width. To do this, you will first need to decide if you are going to install a 4:3 aspect ratio screen (if you are using the projector predominantly for non-HDTV television viewing) or a 16:9 aspect ratio screen (for movies and HDTV).

    If installing a 4:3 screen, take your maximum screen height and multiply it by 1.33 to find your maximum screen width

    If installing a 16:9 screen, take your maximum screen height and multiply it by 1.78 to find you maximum screen width.

    Presto! Now you should have a maximum screen size.

    Step 3. Think about the screen-type and placement.

    Next, you will want to figure out what type of screen you want. Do you want a screen permanently mounted to the wall or a screen that can move up and down?

    You will also need to think about placement of your speakers. You will need to have three speakers placed around the screen for any surround sound system. Do you have room on the sides of the screen? If not, you will have to think about using a smaller screen.

    Setting Up a Room for Front Projection

    Step 4. Projector placement.

    Now that you have a basic idea of what your ideal screen-type will be, it is time to find out if the projector you want will work in your room

    First, find out your projector’s throw ratio. Multiply the screen width by both throw ratio numbers and you’ll have the maximum and minimum distances your projector needs to be placed from the screen. For example, you figured out that you can have a maximum screen width of eight (8) feet for the 16:9 screen you want to place in your room. You think eight feet might be a little too big, so you decide a 7 ½ foot wide screen would work better. The projector you want has a throw ratio of 1.8-2.2:1. So, 7.5 feet * 1.8 equals 13.5 feet, and 7.5 feet * 2.2 equals 16.5 feet, as is indicated in the example below.

    Setting Up a Room for Front Projection

    Next, make sure your room is set up so that you can place a projector in that area (either using a ceiling mount, a stand or a coffee table).

    Step 5. Projector placement Part 2.

    The next part of projector placement is figuring out if you are going to ceiling mount the projector or table/stand mount it.

    A projectors lens is set up so that the projected image will actually appear above the projector itself as shown in the following example.

    Setting Up a Room for Front Projection

    Because all projectors shoot “up” with their standard lenses, they must be inverted to avoid shooting the image into the ceiling as shown in the next example. Projectors with “lens shift” are able to move the image they create up and down, thereby enabling them to be mounted near the ceiling without inverting the projector.

    Setting Up a Room for Front Projection
    Setting Up a Room for Front Projection

    That said, if you are planning on mounting your projector to the back wall on a high shelf, you must figure a way to invert the projector and hang it under the shelf, or purchase a projector with lens shift.

    Step 6. Viewing distance for you audience.

    The last thing to consider is where your audience is going to sit. This all is dependent on your screen width, resolution of the projector you are planning on using and what technology you are using Micro display technologies are all fixed resolution devices, hence the images are actually made up of tiny individual elements called “pixels”. If you stand of sit too close to the projected image, you will actually see the individual elements, effectively destroying the illusion of a seamless image.

    The distance from the image that you need to be, in order to view a seamless image, varies for each technology; it even varies with the resolution of the projector you are watching. Simply put, the higher your projector’s resolution is, the closer you can sit to the image.

    Setting Up a Room for Front Projection

    We suggest the following:

    1. If you have an LCD projector with 600 or less vertical lines of resolution (800 x 600 or 854 x 480), a viewing ratio range of 2-3:1 (V/W) is optimal. If you sit closer that two (2) times the width of your screen, you will start to see the individual picture elements, or a grid pattern known as the “screen door effect,” which gets its name by its resemblance to a screen door having been placed over the image. Conversely, if you sit farther away than three (3) times the width of the screen, the “home theater” effect will be lost.
    2. If you have an LCD projector with more than 600 vertical lines of resolution, we suggest a viewing ratio between 1.8 – 3:1
    3. If you have a DLP™ projector with 600 or less vertical lines of resolution, we suggest using a viewing ratio between 1.8 – 3:1
    4. If you have a DLP™ projector that has a resolution of 1024 x 575 or 1024 x 768, but use it only in 16:9 mode, we suggest using a viewing ratio between 1.6 – 3:1
    5. If you have a DLP™ projector that has a resolution of 1280 x 720, we suggest using a viewing ratio of between 1.4 – 3:1
    6. If you have an LCoS projector, your resolution is going to be above 720 lines, guaranteed. We suggest using a viewing ratio between 1.4 – 3:1 Step 7 (if necessary). What happens if the numbers aren’t working for me?In many cases the numbers you get aren’t going to work. So what to do?Here are some helpful suggestions for some common problems that arise.
      1. My projector won’t produce an image large enough to fill the screen I want to use.
        • Consider moving the projector farther from the screen (if possible).
        • If moving the projector back isn’t possible, consider purchasing a similar model projector with a shorter throw ratio.
        • Some projectors have an optional lens that enables the projector to be moved closer to the screen. This is a very expensive option.
        • The last resort is buying a smaller screen. You must make sure that the new screen size will still be large enough for the viewing ratio calculations.
      2. My viewing distance is shorter or longer than what you suggest.
        • Our suggestions are only guidelines; if your ratio is close but not too far off from our suggestions, you should be fine.
        • If your viewing distance is too far, we’d suggest moving your seating forward if possible.
        • If you can’t move your seating or make your screen larger and you are farther than a 3:1 ratio for your viewing ratio, we suggest either rethinking a front projection system, or resign yourself to the fact that you won’t be getting the home theater experience you might have hoped for.
        • If your viewing distance is too short, we suggest moving your seating back if possible.
        • If your viewing distance is too short, we suggest using a smaller screen if possible.
        • If you can’t move your seating or make your screen smaller and you are much closer than the viewing distance we recommend, we seriously suggest either rethinking a front projection system, or purchasing a rear projection television, plasma screen, or large LCD television.
      3. I need to ceiling mount my projector but I have a really high or slanted ceiling.
        • There are mounting options for every kind of ceiling. Call us and let our account representatives walk you through determining what you might need.

    If you have questions not covered in this section, don’t hesitate to contact us.

  • Learn About the Technologies

    Learn all about the technologies that power projectors, rear projection televisions and plasma displays with our easy-to-understand explanations and diagrams. 

    LCD

    We’ve already learned how a flat panel LCD works in the section Learn about LCD Displays. Now it’s time to learn how the technology works in a projector.

    An LCD optical light engine incorporates three small LCD panels (see Figure 1.): a lamp, filters and a prism to create an image.

    LCD Panels

    White light is provided by way of a lamp. The lamp light is first passed through a polarizing filter, and is then passed through a series of dichroic mirrors (a mirror that reflects only certain wavelengths of light while letting all others pass through), which split the white light into its primary colors: red, green and blue. The three primary colors are then passed through three separate LCD panels and sent to a dichroic prism, which recombines the three primary colors. After the three colors are recombined, the light is passed through the main lens and out of the projector. See Figure 2.

    Inside an LCD Projector

    Each LCD panel controls one of the three primary colors. For example, if we were to show an image of an open green field with a blue sky, the LCD panel that controls red would block all light from passing on to the dichroic prism, while the LCD panel that controls blue would only allow blue light through in the of sky. Meanwhile, the LCD panel for green would do the same for the areas of the green field.

    How does the LCD panel itself work? The light is polarized first. Think of the polarization process as a filter that only accepts light waves that are all traveling on the same plane. In this way, if you were to put two polarized filters back-to-back that filtered the light in opposite planes, all the light would be blocked from passing through.

    This polarized light travels to the LCD panel and passes through a pane of glass to the liquid crystal inside. Liquid crystals have the unique property of bending light as the light travels though. In this manner, the polarized light leaves the liquid crystal, actually traveling on a different plane that when it entered.

    If you apply current to liquid crystal, the crystals align themselves and will not bend the light. Instead the light leaves the liquid crystal on the same plane that it entered.

    If you align a second polarizing filter after the light passes through the liquid crystal, you can block all light from escaping if the light waves are traveling on a plane that the filter blocks. See Figure 3.

    How Liquid Crystal Works

    Each LCD panel has individual cells that are each controlled by a separate transistor that can apply current to the liquid crystal within the cell. The resolution of the display determines the number of cells, or pixels, that the LCD panel has.

    In this way, each panel can control what color each pixel is going to be at any given moment. If a pixel needs to be white, all three panels let through light at their corresponding pixel and the three primary colors are recombined by the dichroic prism to create white light.

    All pixels working together in the projector can then paint a picture in much the same way a printer uses individual dots to make a color image on paper.

    DLP™

    How does a DLP™ projector work? Let’s start with the basics. First, like with all microdisplay technologies, they have a high output lamp that creates white light.

    Color Wheel

    Now white light itself can’t create a full color picture, so there has to be a way of splitting that light into its three primary colors: red, green and blue. DLP™ light engines achieve this by passing the light through a spinning color wheel (see Figure 1). The color wheel is simply a red, green and blue filter that spins in front of the lamp to create the primary colors, one after another.

    We now have red, green and blue light. This light is directed to a small silicon chip called a DMD™ device by Texas Instruments (see Figure 2).

    DMDT

    The DMD ™ device is a small chip that consists of hundreds of thousands of tiny mirrors that can tilt in two directions, designated as on and off positions, at thousands of times per second. See Figure 3.

    Close up of a DMDT

    Each mirror represents one spot, or pixel, of the image. All of these pixels, when combined horizontally and vertically, make up the entire image. This is much in the same way as your printer makes a printed copy for you.

    So how does it make an image? Let’s take that first bit of light that arrives at the DMD™ chip after it passes through the color wheel: red light. At the time the red light strikes the chip, all of the mirrors that correspond to where red should appear within the image will turn “on”. When the pixel is turned “on”, it directs the light out of the lens and to your screen. For the places that contain no red, or no color that is comprised of red, the mirror is turned “off” and the light is then directed away from the lens and to a light collection space within the projector. The DMD™ chip then does the same for the next two colors (blue and green, respectively) in sequence, thereby making up an entire image.

    How does the DMD™ create shades of colors that are not pure red, green or blue, and how does it create an image if the red, green and blue are not shown at the same time?

    It all has to do with timing. The DMD™ displays shades of red by varying the time it keeps red on the screen. The shorter the time on the screen, the less the eye is able to detect the color, resulting in a lighter shade. It creates colors and whites the same way. Displaying all three primary colors, one after another for the same time period, produces white. If you wish to display a shade of gray, then each color is produced for a shorter time period. To produce colors, the DMD™ will vary the amount of time each color is on the screen to produce different colors at different shades.

    DLPT Optical Engine

    LCoS

    (a.k.a D-ILA, SXRD and Reflective LCD)

    Liquid crystal on silicone (LCoS) technology has a few variances that are in the market place; JVC calls its version D-ILA, while Sony has named its version SXRD. Nonetheless, all versions work in pretty much the same manner.

    Think of LCoS technology as an LCD on a silicone wafer. To build on that, let’s start with how a liquid crystal in a LCoS panel works.

    Polarized light is first sent to the LCoS panel. Think of the polarization process as a filter that only accepts light waves that are all traveling on the same plane. In this way, if you were to put two polarized filters back-to-back that filtered the light in opposite planes, all of the light would be blocked from passing through.

    This polarized light travels to the LCoS panel and passes through a pane of glass and transparent electrode to the liquid crystal inside.

    Liquid crystals have the unique property of bending light as the light travels though them. In this manner, the polarized light leaves the liquid crystal, actually traveling on an entirely different plane that when it entered. In the case of an LCoS panel, the light is reflected off the silicone layer behind the liquid crystal and back out of the front of the LCoS panel.

    If you apply current to liquid crystal, the crystals align themselves and will not bend the light. Instead, the light leaves the liquid crystal on the same plane that it entered.

    If you align a second polarizing filter to filter the light that was reflected through the LCoS panel, you can block all light from escaping if the light waves are traveling on a plane that the filter blocks. See Figure 1.

    Inside an LCoS Panel

    Now we can talk about how the panels are used in an optical engine to produce and image.

    An LCoS optical light engine incorporates three small LCoS panels (AKA SXRD or D-ILA panels; see Figure 2.), a lamp, filters and prisms to create an image.

    LCoS Panel

    White light is provided by way of a lamp. The lamp light is first passed through a dichroic mirror (a mirror that reflects only certain wavelengths of light while letting all others pass through) that splits the white light into yellow and blue light.

    The yellow light is then passed on to an additional dichroic mirror that splits the yellow light into red and green light.

    The red, green and blue light is then passed through polarizing filters before being sent to directional prisms that reflect light coming from a certain direction, but allow the same light to pass through if coming from a different direction. These prisms are used to bounce the light off of the three LCoS panels.

    After the red, green and blue light is bounced off the LCoS panels, it is sent to another dichroic prism, which recombines the three primary colors. After the three colors are recombined, the light is passed through the main lens and out of the projector. See Figure 3.

    Inside an LCoS Projector

    Each LCoS panel controls one of the three primary colors. For example, if we were to show an image of an open green field with a blue sky, the LCoS panel that controls red would block all light from passing on to the dichroic prism, while the LCoS panel that controls blue would only allow blue light through for the areas of sky. Meanwhile, the LCoS panel for green would do the same for the areas of the green field.

    Each LCoS panel has individual cells that are each controlled by a separate transparent transistor that can apply current to the liquid crystal within the cell. The resolution of the display determines the number of cells, or pixels, that the LCoS panel has.

    In this way, each panel can control what color each pixel is going to be at any given moment. If a pixel needs to be white, all three panels let through light at their corresponding pixel, and the three primary colors are recombined by the dichroic prism to create white light.

    All pixels working together in the projector can then paint a picture in much the same way a printer uses individual dots to make a color image on paper.

  • Projector brightness: How Bright Do I Need It?

    Projector brightness is rated in lumens. A lumen rating indicates the overall brightness that a projector is able to produce. Lumens are actually dimensionless, so the lumen output of the projector is static and has nothing to do with the size of the image. However, the size of the image has everything to do with how bright the image you see is. For example, the larger the image is that you are trying to create, the brighter the projector will need to be if you want to overcome ambient light and still see a nice, vibrant image.

    Below is a set of standard rules intended to help you select a projector powerful enough to overcome the environment you’ll use it in.

    Selecting a projector that is equal to or greater than our lumen/brightness recommendations will not be detrimental with regard to performance, however it may cost you more money than you need to spend. These rules are simply guidelines to use for a bright, high-contrast image, but they are not set in stone. Projectors with lower outputs than our lumen/brightness recommendations will still display a viewable image, but they may not pack the “punch” that many come to expect when watching business related materials.

    If you have further questions, or will use the projector in a manner different than described below, please don’t hesitate to call us for further assistance at 800-649-9809, Monday through Friday between the hours of 8 a.m. and 6 p.m. (ET). You may also email us at: info@theprojectorpros.com.

    1. I am creating an image that is = 6 feet in width:
      1. In a 100% light controlled room – 1000 lumens should be sufficient
      2. In a room with some ambient light, but no direct lighting on the space you plan to project the image – 1000 lumens should be sufficient
      3. In a room with the lights on, but no light directly over the area where you will project the image – 1000 to 1200 lumens should be sufficient
      4. In a room with bright ambient light – 1400 to 1500 lumens should be sufficient
      5. I don’t know how bright the room will be, but I do know that my image size won’t surpass six (6) feet – 1500 lumens to ensure that you will overcome all lighting conditions should be sufficient.Projector brightness: How Bright Do I Need It?
    2. I am creating an image that is between six (6) and eight (8) feet in width:
      1. In a 100% light controlled room – 1000 to 1200 lumens should be sufficient
      2. In a room with some ambient light, but no direct lighting on the space you plan to project the image – 1200 to 1400 lumens should be sufficient
      3. In a room with the lights on, but no light directly over the area where you will project the image – 1300 to 1500 lumens should be sufficient
      4. In a room with bright ambient light – 1500 to 1800 lumens should be sufficient
      5. I don’t know how bright the room will be, but I do know that my image size won’t surpass eight (8) feet – 1800 lumens to ensure that you will overcome all lighting conditions should be sufficient
    3. I am creating an image that is over eight (8) feet wide but less than ten (10) feet wide:
      1. In a 100% light controlled room – 1500 lumens should be sufficient
      2. In a room with some ambient light, but no direct lighting on the space you plan to project the image – 1500 to 1800 lumens should be sufficient
      3. In a room with the lights on, but no light directly over the area where you will project the image – 2000 lumens should be sufficient
      4. In a room with bright ambient light – 2000 to 2500 lumens should be sufficient
      5. I don’t know how bright the room will be but I do know that my image size won’t surpass ten (10) feet. – 2500 lumens to ensure that you will overcome all lighting conditions should be sufficient
    4. I’m creating an image over ten (10) feet wide but less than fourteen (14) feet wide:
      1. In a 100% light controlled room – 2000 lumens should be sufficient
      2. In a room with some ambient light, but no direct lighting on the space you plan to project the image – 2000 to 2300 lumens should be sufficient
      3. In a room with the lights on, but no light directly over the area where you will project the image – 2300 to 2700 lumens should be sufficient
      4. In a room with bright ambient light – 2700 to 3200 lumens should be sufficient
      5. I don’t know how bright the room will be, but I do know that my image size won’t surpass fourteen (14) feet – 3200 lumens to ensure that you will overcome all lighting conditions should be sufficient
    5. I’m creating images for very large audiences that will surpass fourteen (14) feet in width.
      1. Contact us directly. We’ll need additional information to help you select the most appropriate projector for your needs.

    Many people will find that their application lies within two different categories, or they may not know the size of the image they’ll display. If you do know the size range of the images you will need to display, you’ll need to select a projector that can produce the largest images in your range. If you don’t know the image size you’ll need, please refer to the below chart for help.

    1. Standard size room with an eight (8) foot ceiling – Maximum width is six (6) feet wide using a business projector with a 4:3 aspect ratio (not widescreen)
    2. Rooms with nine (9) foot ceilings – Maximum width is 7.33 feet wide using a business projector with a 4:3 aspect ratio (not widescreen)
    3. Rooms with ten (10) foot ceilings – Maximum width is 8.66 feet wide using a business projector with a 4:3 aspect ratio (not widescreen)
    4. Rooms with twelve (12) foot ceilings – Maximum width is 11.33 feet wide using a business projector with a 4:3 aspect ratio (not widescreen)
    5. Rooms with ceilings over twelve (12) feet are usually closer to twenty (20) feet; for this scenario, please use the extended table below:
    6. How far is the furthest person back from the screen? Take that distance and divide it by 1.5 to 2.5 and you’ll have a range of screen widths to use. The larger the width you’ll choose, the better those seated in the back will see the image.

    Example: The furthest person in back is 20 feet away.
    20 / 2.5 = 8 feet wide and 20 / 1.5 = 13.33 feet wide. You will need at least a nine (9) foot ceiling to display an eight (8) foot wide screen and at least a fourteen (14) foot high ceiling to display a 13.33 foot wide image.

  • Aspect Ratio Thoughts

    We initially covered aspect ratios back in the section Resolutions and Aspect Ratios Explained In this section, we will go in-depth about how projectors display different aspect ratios.

    Scenario One. You are going to buy a widescreen projector and would like to know what to expect when using it to view non-native aspect ratios.

    The first thing to understand when purchasing a widescreen home theater projector is that almost no content is actually in a 16:9 (1.78:1) aspect ratio. Therefore, almost all of the material you watch will be formatted to fit onto your screen (with black bars displayed on top and bottom or on the left and right of the image).

    When watching standard definition television (4:3 or 1.33:1 aspect ratio material), you generally have the option of either watching the material in its native aspect ratio or stretching the image. Most home theater projectors will usually give the option of blowing up the image to fill the entire screen, thus cutting off some of the top and bottom of the image, or subtly stretching the image horizontally. And, both options have serious flaws: either you’ll chop off some of the image or you’ll stretch the image and cause image distortion. The best option is to leave the image alone.

    Example 1 shows the difference between stretching the image horizontally versus leaving the signal as a 4:3 image.

    4:3 Image converted to a 16:9 Image
    Example 1

    Watching DVDs, or other material that is film-based, will result in your discovering that movies are seldom, if ever, filmed in a 16:9 (1.78:1) aspect ratio. Instead, they are generally recorded in a 1.85:1 or 2.35:1 aspect ratio, which is actually wider than the aspect ratios of widescreen projectors or televisions. When watching material in a 1.85:1 or 2.35:1 aspect ratio on your widescreen projector, your image will look like example 2.

    Different Aspect Ratios on a 16:9 Screen
    Example 2

    Whenever a projector adds black bars to an image, you are no longer using the full resolution of your projector. If buying a widescreen projector, make sure to match the resolution of the projector to the resolution of the content you will most likely watch to ensure the best results.

    If you aren’t watching HDTV often, and don’t plan on converting to it in the next few years, an 854 x 480 projector will suffice for watching standard definition television and DVDs as it most closely matches the resolution of DVD.

    If most of your viewing is DVD and standard definition television, and you do watch some HDTV programming, a 1024 x 575 or 960 x 540 projector will give you wonderful clarity for both standard definition and high definition sources.

    If you love your HDTV now and want something that takes full advantage of it, then a 1280 x 720 or greater resolution projector is what you need. But keep in mind that standard definition sources will generally look crisper on a projector that better matches its resolution.

    Scenario Two. You are going to buy a 4:3 aspect ratio business projector to use for home theater and would like to know what to expect when using it to view non-native aspect ratios.

    Mapping widescreen images onto a 4:3 projector can pose unique challenges and a consumer needs to be aware of them.

    Micro display projectors all have a native resolution that can’t be changed. If you are buying a 4:3 projector and plan to watch widescreen images on it, you must understand that you are going to lose a significant amount of vertical resolution in the process. Let’s look at a native 4:3 aspect ratio 800 x 600 (SVGA) projector as an example.

    If you watch a 16:9 (1.78:1) aspect ratio image on an SVGA projector, your total vertical resolution available drops from 600 lines to 450 lines as seen in Example 3.

    Resolution Change from Letterboxing
    Example 3

    If you watch even wider screen images on an SVGA projector, your vertical resolution drops even further. Example 4 shows a 2.35:1 image on an SVGA projector.

    Resolution Change from 2:35:1 Letterboxing
    Example 4

    Problems can arise when you try to watch HDTV images on a projector with too low of a resolution. A 1280 x 720 image from a 720p HDTV signal would have to be scaled down to 800 x 450 on an SVGA projector. That is a staggering 61% loss of resolution! The situation would be worse when watching a 1080i HDTV signal.

    Here is a quick table of the 16:9 (1.78:1) resolutions for common 4:3 aspect ratio business projectors. Remember: always choose a projector that best matches the resolution of the source material you watch the most.

    An SVGA (800 x 600) projector is actually 800 x 450 when viewing a 16:9 image.

    An XGA (1024 x 768) projector is actually 1024 x 575 when viewing a 16:9 image.

    An SXGA (1365 x 1024) projector is actually 1365 x 766 when viewing a 16:9 image.

  • DLP™

    How does a DLP™ projector work? Let’s start with the basics. First, like with all microdisplay technologies, they have a high output lamp that creates white light.

    Now white light itself can’t create a full color picture, so there has to be a way of splitting that light into its three primary colors: red, green and blue. DLP™ light engines achieve this by passing the light through a spinning color wheel (see Figure 1). The color wheel is simply a red, green and blue filter that spins in front of the lamp to create the primary colors, one after another.

    Color Wheel
    Figure 1

    We now have red, green and blue light. This light is directed to a small silicon chip called a DMD™ device by Texas Instruments (see Figure 2).

    DMDT
    Figure 2

    The DMD ™ device is a small chip that consists of hundreds of thousands of tiny mirrors that can tilt in two directions, designated as on and off positions, at thousands of times per second. See Figure 3.

    Close up of a DMDT
    Figure 3

    Each mirror represents one spot, or pixel, of the image. All of these pixels, when combined horizontally and vertically, make up the entire image. This is much in the same way as your printer makes a printed copy for you.

    So how does it make an image? Let’s take that first bit of light that arrives at the DMD™ chip after it passes through the color wheel: red light. At the time the red light strikes the chip, all of the mirrors that correspond to where red should appear within the image will turn “on”. When the pixel is turned “on”, it directs the light out of the lens and to your screen. For the places that contain no red, or no color that is comprised of red, the mirror is turned “off” and the light is then directed away from the lens and to a light collection space within the projector. The DMD™ chip then does the same for the next two colors (blue and green, respectively) in sequence, thereby making up an entire image.

    How does the DMD™ create shades of colors that are not pure red, green or blue, and how does it create an image if the red, green and blue are not shown at the same time?

    It all has to do with timing. The DMD™ displays shades of red by varying the time it keeps red on the screen. The shorter the time on the screen, the less the eye is able to detect the color, resulting in a lighter shade. It creates colors and whites the same way. Displaying all three primary colors, one after another for the same time period, produces white. If you wish to display a shade of gray, then each color is produced for a shorter time period. To produce colors, the DMD™ will vary the amount of time each color is on the screen to produce different colors at different shades.

    DLPT Optical Engine
    Figure 4
  • LCD

    We’ve already learned how a flat panel LCD works in the section Learn about LCD Displays. Now it’s time to learn how the technology works in a projector.

    An LCD optical light engine incorporates three small LCD panels (see Figure 1.): a lamp, filters and a prism to create an image.

    LCD Panels
    Figure 1

    White light is provided by way of a lamp. The lamp light is first passed through a polarizing filter, and is then passed through a series of dichroic mirrors (a mirror that reflects only certain wavelengths of light while letting all others pass through), which split the white light into its primary colors: red, green and blue. The three primary colors are then passed through three separate LCD panels and sent to a dichroic prism, which recombines the three primary colors. After the three colors are recombined, the light is passed through the main lens and out of the projector. See Figure 2.

    Inside an LCD Projector
    Figure 2

    Each LCD panel controls one of the three primary colors. For example, if we were to show an image of an open green field with a blue sky, the LCD panel that controls red would block all light from passing on to the dichroic prism, while the LCD panel that controls blue would only allow blue light through in the of sky. Meanwhile, the LCD panel for green would do the same for the areas of the green field.

    How does the LCD panel itself work? The light is polarized first. Think of the polarization process as a filter that only accepts light waves that are all traveling on the same plane. In this way, if you were to put two polarized filters back-to-back that filtered the light in opposite planes, all the light would be blocked from passing through.

    This polarized light travels to the LCD panel and passes through a pane of glass to the liquid crystal inside. Liquid crystals have the unique property of bending light as the light travels though. In this manner, the polarized light leaves the liquid crystal, actually traveling on a different plane that when it entered.

    If you apply current to liquid crystal, the crystals align themselves and will not bend the light. Instead the light leaves the liquid crystal on the same plane that it entered.

    If you align a second polarizing filter after the light passes through the liquid crystal, you can block all light from escaping if the light waves are traveling on a plane that the filter blocks. See Figure 3.

    How Liquid Crystal Works
    Figure 3

    Each LCD panel has individual cells that are each controlled by a separate transistor that can apply current to the liquid crystal within the cell. The resolution of the display determines the number of cells, or pixels, that the LCD panel has.

    In this way, each panel can control what color each pixel is going to be at any given moment. If a pixel needs to be white, all three panels let through light at their corresponding pixel and the three primary colors are recombined by the dichroic prism to create white light.

    All pixels working together in the projector can then paint a picture in much the same way a printer uses individual dots to make a color image on paper.

  • Learn About Home Theater — Projectors

    This section is dedicated to providing specific information about home theater as it applies to front projection. We recommend that you read the general section first so you become familiar with the terminology.

    As with our other sections, we include pictures and diagrams to help reinforce the learning process — and to make it a little more fun.

    If you have questions or would like to more information about a subject, please call us at 1-800-649-9809 or email us at info@theprojectorpros.com.

    Is Front Projection Right for Me?

    The first and most fundamental question about front projections is, “is it right for me?” It depends. Let’s run through the criteria we think is necessary to go forward with a front projector purchase.

    Controlled lighting — Front projectors throw light onto a screen. The projected light is then reflected back to your eye.

    Reflected Light

    The problem with this type of set up is that the screen itself isn’t choosey about what light it reflects back to your eye. If you have lights on in the room or light spilling in from windows, that light combines with the reflected light of the projector and washes out the image.

    The question that logically follows is, “how much stray light is too much?” A normal home theater projector usually has a brightness rating somewhere in the range of 800-1500 lumens. Given a projector with that kind of light output, the rule of thumb would be that if a room has enough light to read in, it is probably too bright for a standard home theater front projector. You don’t need to have the room perfectly dark, although the darker the room, the better the image quality you will get out of your projector

    If your room just can’t be configured to control ambient light, there are still a couple of options left if you are dead set on using a front projector. The options are as follows:

    Buy a brighter home theater projector — To overcome some ambient light, you could buy a much brighter projector. The problem here is that compromises must be made. To gain brightness in a home theater projector, you will generally lose contrast and shadow detail. For most people, this is a fair compromise, but be warned that high lumen home theater projectors will also carry a hefty price tag, especially if you want to have a DLP™ projector.

    Buy a brighter dual purpose projector — Another option to gain a brighter projector is to buy a business projector for your home theater. Business projectors tend to be geared towards brightness, and away from color accuracy and contrast. If you choose to go this route, you need to keep the following factors in mind:

    1. Business machines are in a 4:3 aspect ratio. Most will show any widescreen image, but you lose vertical resolution. 
      1. An SVGA (800 x 600) projector will give you an 800 x 450 resolution when using it in 16:9 mode. There will be black bars on top and bottom of the image
      2. A XGA (1024 x 768) projector will give you a 1024 x 575 resolution when using it in16:9 mode. There will be black bars on top and bottom of the image.
      3. An SXGA (1365 x 1024) projector will give you a 1365 x 766 resolution when using it in16:9 mode. There will be black bars on top and bottom of the image.

    2. The most notable difference between an LCD business projector and an LCD home theater projector will be the difference in resolution. Other differences can be in menu features that allow for fine tuning the image, although some LCD business projectors can rival home theater projectors in functionality.
    3. The differences between a home theater DLP™ and a business DLP™ are vast in number. The light engine in a business DLP™ is set up for brightness and the sacrifice of color saturation and color accuracy. You’ll also notice the same resolution and functionality differences in DLP™ projectors as with the LCD projectors.
    4. Brightness ratings for business projectors are calculated while viewing images from a computer. When showing video, the brightness produced will not be close to the stated lumen rating of the projector. There is no numerical calculation available to figure out the lumen output showing video because each technology is different, and each model will vary widely depending on how the manufacturer set up the projector at the factory. As a general rule, expect at least a 30% drop in brightness.

    All this isn’t to say that business machines shouldn’t be used in a home theater setting, just that you have to be prepared to accept shortcomings in the brightness you are looking for. Consult a sales professional for the best business machines that can be used for home theater. They will be the best resources to steer you towards models that are set up specifically for dual-purpose multimedia.

    Room Dimensions — Your room dimensions and layout are other major obstacles to buying a front projector. We will cover specifics of how to set up a room later, but will give you a starting point here.

    Front projectors need room to throw a large image. If you want to have a true home theater experience, we suggest that you start with a moderately large room. The whole point of purchasing a front projector is to give a theater-like experience; this is lost if your room dimensions prevent you from projecting an image larger than six (6) feet wide without costly short throw lenses or complicated, costly rear projection set ups. We suggest keeping it simple.

    Think about the room you want to place your projector in. Is there a place for at least a six (6) foot wide screen? Is there available space for proper placement of your surround sound speakers? Is the seating going to be too far away from the screen, thereby ruining the large screen experience, or are they going to be too close preventing viewers from seeing the entire screen without looking from side to side?

    If you have a room too small or too crowded, we would suggest looking into the options of a flat panel display or a rear projection television.

    For detailed instructions on how a room should be set up, please refer to our section “Setting Up a Room for Front Projection.”

    DLP™ vs. LCD vs. LCoS

    The most common questions about front projectors center on the different technologies that they use. Which is better? That depends on what you are looking for. In this section will we compare the technologies as they relate to front projection. We will discuss how the technologies work in greater detail in the Learn About The Technologies section.

    Digital Light Processing™ (DLP™) — DLP™ is a Texas Instruments technology that uses micro mirrors to project an image. There are three distinct types of DLP™ light engines: three chip; single chip for home theater and single chip for business. We will cover the pros and cons for each.

    Three chip DLP™ — Pros:

    1. Perfect color accuracy.
    2. Good contrast; much greater than film theaters.
    3. Good shadow detail.
    4. Can provide high brightness compared to the limited brightness of single chip versions.
    5. Overall image quality deemed as the best of any type of micro display technology.
    6. Same technology as projectors installed in digital theaters.
    7. Pure digital technology.

    Three chip DLP™ — Cons:

    1. Very expensive compared to the other technologies. Prices start at around $20k.
    2. Lower contrast than single chip versions.
    3. Generally larger and always louder than single chip versions.
    4. Lamps usually don’t last as long.

    Single chip DLP™ for home theater — Pros:

    1. Fantastic color accuracy.
    2. The best contrast ratios and shadow detail.
    3. Generally very quiet.
    4. Very little space between each pixel creates a very smooth image, even when using lower resolution projectors.
    5. Best overall image quality available for under $10k.
    6. Very few, if any, dead pixels.
    7. Light engine failures are very rare so repairs are less costly than other technologies.
    8. Technology doesn’t degrade over time. With proper routine maintenance, DLP™ projectors consistently provide just-out-of-the-box performance. (DLP™ is the only technology that makes this claim).
    9. Color uniformity is the best of the technologies.

    Single chip DLP™ for home theater — Cons:

    1. It is more expensive than LCD technologies given comparable projector resolution and brightness.
    2. Home theater DLP’s only reach a maximum of 1500 lumens of brightness.
    3. On some DLP™ projectors, viewers can detect a color breakup effect called the “rainbow” effect. This rarely occurs with home theater DLP’s.

    Single chip DLP™ for business — Pros:

    1. Provides higher brightness than home theater DLP’s.
    2. Excellent contrast and shadow detail.
    3. Generally produces reduced noise levels.
    4. Very little space between each pixel creates a very smooth image even when using lower resolution projectors.
    5. Very few, if any, dead pixels.
    6. Light engine failures are very rare so repairs are less costly than other technologies.
    7. Technology doesn’t degrade over time. With proper routine maintenance, DLP™ projectors consistently provide just-out-of-the-box performance. (DLP™ is the only technology that makes this claim).
    8. Color uniformity is the best of the technologies.
    9. Cheaper to purchase – based on resolution and brightness – than true home theater DLPs.

    Single chip DLP™ for business — Cons:

    1. Color saturation is not as good as LCD or home theater DLP™ machines.
    2. Color separation effect, AKA “rainbow effect,” can be apparent on these projectors and can be distracting to watch, although most people don’t notice the effect.
    3. Advanced menu screens for image adjustments are rare in business machines, although some manufacturers do offer them.
    4. Most, but not all, business machines won’t offer HDCP enabled digital inputs.
    5. These machines are only offered in 4:3 aspect ratios.
    6. True 720p resolution projectors not offered.

    LCD — LCD or liquid crystal displays are the oldest type of micro display technology used in front projection. Since the only real differences between an LCD projector for home theater and one built for business are the resolution and menu options, we won’t differentiate between the two here.

    Pros:

    1. Can be very bright even in home theater applications.
    2. True high definition models are the least costly of any technologies with 720p models starting at under $2k.
    3. Great color saturation.
    4. Home theater models are usually feature-rich.
    5. 1000 lumen and lower models will usually have long lasting lamps.

    Cons:

    1. Dead pixels are common.
    2. Contrast ratios are lower than those on DLP™ projectors.
    3. Shadow detail and absolute black levels fall short of DLP™ powered projectors.
    4. Panel convergence problems (where the three LCD panels don’t align properly producing a noticeable color halo around each pixel) are common.
    5. LCD panels are organic and lose image quality over time. The less the machine is used each day, the less of a problem this is. Projectors that are used for over eight (8) hours a day can exhibit problems fairly quickly.
    6. Color uniformity across the image is lower than that of DLP™ powered projectors.

    LCoS — LCoS, or liquid crystal on silicone projectors, came along at about the same time as DLP™ powered projectors and have a much smaller market share than either DLP™ or LCD in the home theater or business machine markets. LCoS technology is also referred to as reflective LCD, while individual manufacturers use their own names. For example, JVC refers to its LCoS light engines as “D-ILA.”

    Pros:

    1. LCoS resolutions tend to start at SXGA enabling native 720p high definition images to be shown.
    2. Like LCD, LCoS machines can be very bright.
    3. Offers a very smooth, film-like image due to its pixel structure.
    4. Great color saturation and accuracy.

    Cons:

    1. Can be pricey, although based on resolution, the cost is not much more than that of DLP™ home theater projectors.
    2. Dead pixels are more visible than with other technologies and happen as often as with LCD’s.
    Learn About Home Theater — Projectors

    How Will Different Video Sources Look on a Front Projector?

    An important thing to remember when building a front projection system is to keep your expectations reasonable. For example, it’s natural to assume that when combining a high definition projector with a state-of-the-art theater room that all viewing materials are guaranteed to look stunning. This is not always the case. Digital projectors can look stunning with the right source material, but the quality of the source material is paramount in obtaining a movie theater-like performance from any projector

    Here is a brief overview of what to expect from different video sources when viewed with a front projector.

    Standard Over-the-Air Broadcasts (NTSC): If you opt for an old antenna to view standard definition television, your viewing experience is going to depend entirely on your reception. You can expect a fairly good image if you receive a strong signal, but this is rarely the case at all times. Because over-the-air analog signals are so prone to interference from a number of factors ranging between weather to sunspots, receiving a quality image at all times is difficult, if not impossible. When the reception is poor, ghosting, snow and a host of other problems can occur, and “blowing up” these eyesores to sizes of over five feet in width only exacerbates the issue. In short, if using an antenna, don’t expect too much out of your projector.

    Cable Television – Analog channels: Cable television is obviously the most common video source for any video display. The thing to remember is that even with digital cable, all channels below 100 are still analog. How well these analog channels will look varies widely based on how far away you are from the point of transmission and how well your particular cable company is at shielding signals on the way to your home. Generally these channels tend to be of rather low quality. Expect snow, ghosting and an assortment of other problems that are only maximized when viewing them with displays larger than 35 inches diagonally. As with over-the-air broadcasts, expect the image to look worse than it would on your smaller television.

    Cable Television – Digital channels (NTSC): Digital cable channels – those over channel 100, will appear bright, sharp and colorful regardless of the projector resolution you choose. Hopefully the proliferation of digital television will speed cable companies’ conversions of the most popular analog stations to digital.

    Analog Satellite Television (NTSC): There are still many of the old-style, larger satellite dishes around rural America. If you are still using an analog satellite dish, expect the same type of results as with over-the-air and analog cable broadcasts.

    Digital Satellite Television (NTSC): Newer digital satellite services offer 100% digital television. Most of the more common stations still originate from an analog source, but are converted into a digital signal before being transmitted to your home, vastly reducing, but not eliminating, problems with an analog transmission. Expect similar results as you would from digital cable channels, although channels that were originally analog (such as WGN, WTBS, etc.) can have some quality issues.

    VHS: VHS players/recorders are analog and very low resolution. Even if you have a higher resolution S-VHS player, don’t expect a wonderful image from a front projector. We suggest avoiding VHS players of any kind as your primary source for theater viewing materials. If you do have older tapes that you want to view or want to set up a VHS player for the kids to watch, we suggest purchasing a VHS player with an S-video output and using only the highest quality cable to ensure that you’re getting the best image possible. We also suggest that if you have a large library of camcorder videos on tape, get them converted to a digital medium as soon as possible.

    DVD: DVD players are digital devices whether or not they actually have digital outputs. DVD will look great on any projector. Expect clear, colorful, vibrant images. Just how clear, vibrant and colorful will depend on the projector.

    High Definition Television (HDTV): Obviously HDTV is going to look great regardless of the source or what projector you buy. Exactly how good it looks can depend on a few factors including:

    1. How close the projector resolution is to that of the HDTV signal. The less the projector has to scale an image down, the better.
    2. How much compression was used to transmit the signal can greatly affect the overall image clarity. Compression rates vary with each cable and satellite company, so results can vary across the country. There are many internet forums that discuss each company’s merits if you’d like to research your cable or satellite company before going to HDTV.

    Picking the Right Projector

    1. What is my budget?The first thing to do when choosing a front projector is to determine how much you’d like to spend for the projector. To do this with some accuracy, you must take into consideration the costs for cables, mounts, screen and any audio equipment you may need. Once you have a number in mind, you’ll narrow down your shopping list and have a clearer picture of your options. Here are some examples:
      1. Let’s say you have $10,000 to spend on just the projector. The sky is pretty much the limit. With this budget, you can take a close look at all of the available technologies to see which will offer you the most bang for your buck.
      2. You have $2500 to spend. 720p DLP™ projectors and LCoS projectors will be out of your price range. You’ll need to choose between a mid-resolution DLP ™ projector (1024 x 575), or go with a higher-resolution LCD projector.
      3. You have $1000 to spend. Your choices will be limited to widescreen 480p projectors — in both LCD and DLP™ technologies.
    2. Choose a technology Once you have a better idea of what technologies you can afford, it will be time to make your actual choice. First, read everything you can about how the technology works. Carefully review the pros and cons of your projector to determine if your projector is right for your environment.As we’ve already mentioned, if you have an ultra-bright room without any practical means of reducing ambient light, then the room itself will dictate the technology you must use.
    3. Choosing a brand and model The next step is to plan the layout of your front projection room. You will need to figure out a few things before looking at particular projector models including:
      1. The distance you’ll need to place the projector from where you would like to place your screen.
      2. The maximum width you would like your image to be.
      3. The distance your audience will be from the screen.These measurements will help you figure out which projector will work for your particular room setup.Once you know the specs you need from your front projector, you can establish which makes and models match your individual needs. If you are deciding between manufacturers, we would suggest choosing only manufacturers that actually make the products they sell — not those that “re-label” other companies’ products, and manufacturers that have been in the projector business for a significant period of time.Many major companies have dabbled in projectors and then abruptly left the business, leaving owners of their products with little, if any, support. If you are unsure about a company, investigate it further — talk to one of our representatives. Our team has substantial knowledge of today’s front projector manufacturers.
  • Color Temperature Controls

    The color temperature settings control the way in which a projector projects white and color. A true white is around 6500° Kelvin; if the projector is told to display white at a higher color temperature, whites will tend to have a bluish hue to them. If you set the projector to a lower setting, whites will tend to have a more reddish hue.

    Why change the color temperature at all? First, projectors can come from the factory with their color temperatures set too high or too low for your tastes. Secondly, different sources will look better at different color temperatures. Computer images can look brighter and more vivid at a higher color temperature while movies are better at or below 7000° Kelvin. Generally projectors’ setting will range between 5500° K- 9000°K, although they are not usually marked as degrees Kelvin. Typically, you will find color temperature controls labeled as low, mid and high, or warm, normal and colder.

    Color Temperature Controls

    Color temperature is defined in scientific terms as a black body — a hypothetical object that absorbs all of the energy that falls on it. When heated, the black body turns to color. At first, it will turn red, then yellow, and ultimately blue and violet. The temperature at which the black body matches the color of a given light source is said to be the color temperature of that light. The following chart gives examples of some common color temperatures.

  • LCD panels: How Does It Work?

    LCD (Liquid Crystal Display) panels are “transmissive” displays, meaning they aren’t their own light source but instead rely on a separate light source and then let that light pass through the display itself to your eye.

    We can start to describe how an LCD panel works by starting with that light source. The light source is a very thin lamp called a “back light” that sits directly behind the LCD panel as shown in Figure 1.

    LCD Panel Inside
    Figure 1

    The light from the backlighting then passes through a polarizing filter (a filter that aligns the light waves in a single direction). From there the now polarized light then passes through the actual LCD panel itself. The liquid crystal portion of the panel either allows the polarized light to pass through or blocks the light from passing through depending on how the liquid crystals are aligned at the time the light tries to pass through. See Figure 2.

    How Liquid Crystal Works
    Figure 2

    The liquid crystal portion or the panel is spit up into tiny individual cells that are each controlled by a tiny transistor to supply current. Three cells side by side each represent one “pixel” (individual picture element) of the image. An 800 x 600 resolution LCD panel would have 480,000 pixels and each pixel would have three cells for a total of 1,440,000 individual cells.

    Red, green and blue are the primary colors of light. All other colors are made up of a combination of the primary colors. An LCD panel uses these three colors to produce color which is why there are three cells per pixel — one cell each for red, green, and blue.

    Once the light is passed through the liquid crystal layer and the final polarizing filter it then passes through a color filter so that each cell will then represent one of the three primary colors of light. See Figure 3.

    LCD Panel Inside
    Figure 3

    The three cells per pixel then work in conjunction to produce color. For example, if a pixel needs to be white, each transistor that controls the three color cells in the pixel would remain off, thus allowing red, green and blue to pass through. Your eye sees the combination of the three primary colors, so close in proximity to each other, as white light.

    If the pixel needed to be blue, for and area of an image that was going to be sky, the two transistors for the red and green cells would turn on, and the transistor for the blue cell would remain off, thus allowing only blue light to pass through in that pixel.

    We hope this straightforward explanation is enough. If you have further questions, please email us at info@theprojectorpros.com.

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