Projectors can be used for a variety of purposes, whether in the classroom for a lecture or in a conference room for a business meeting. They are often used in home theater setups, because they can create a larger image than a television and more readily accommodate larger numbers of viewers. There are two main types of projectors, defined by the technology they use: LCD (liquid crystal display) projectors and DLP (digital light processing) projectors. This guide will briefly explore color theory and light, as well as terms to know regarding projector technology, before examining the differences between the two types of projectors and the benefits and disadvantages to each. Consumers can find projectors at specialty camera shops, electronics retailers, and big-box stores, as well as through Internet marketplaces like eBay.
Color Theory and Light
Knowing a bit about color theory can translate into a better understanding of how projection technologies work. Light works on an additive theoretical model, meaning that the different colors of light combine to create white. By contrast, paints and inks work on a subtractive model in which white is created by the absence of these other colors.
Many children are taught that the primary colors are red, blue, and yellow, because these combine to create all other colors, except white. While this is true, in the professional world, the primary colors in the subtractive model are cyan (a light blue), magenta (a pinkish red), and yellow. Most printing devices also use black inks and pigments. The full complement of colors is commonly referred to as "CMYK."
Conversely, the primary colors in the additive model are red, green, and blue, collectively dubbed "RGB." These three colors combine to form white light. Electronics like projectors, televisions, and computer screens rely on the RGB model, using arrangements of pixels to create all other colors (except black) for the human eye.
DLP and LCD Projectors Terminology
A variety of factors contribute to the overall performance of a projector and which applications it is suited to, beyond the technology used. These include the brightness and contrast ratio of the projector. Consumers should also consider the distance across which the projector can send an image.
Brightness refers to the amount of light generated by the projector, measured in ANSI lumens. The brightness level indicates how well the projector will function in rooms with ambient light. In spaces where low lighting is an option, a projector does not need a high brightness, so a rating of 2000 ANSI lumens or less will suffice. However, in brightly lit spaces, such as classrooms and conference rooms, a projector with a brightness of 3500 ANSI lumens or more is ideal. In addition, larger images require higher brightnesses, as the light is diffused across a greater space.
Contrast ratio refers to the difference in brightness between the brightest white and the darkest black, so a contrast ratio of 2,000:1 means that the white is 2,000 times brighter than the black. Contrast is especially important for videos, but less so for data presentations. However, there are no standards for measuring contrast ratio, so this can differ significantly across manufacturers. Typically, the contrast ratio given is the on-off ratio, which is a simple comparison of the brightest white and darkest black. However, there are also ANSI contrast ratios, which are much lower than on-off ratios, and dynamic contrast ratios, which are much higher.
Throw distance refers to the distance between the projector and the screen, or how far the projector can "throw" the image. This affects how large the projected image can be, as well. Typically, the shorter the distance, the smaller the screen. Conversely, a longer throw distance equals a larger image. Some projectors support zoom lenses that can help reduce the limitations of the throw distance by allowing a larger image over a short distance or a smaller image over a long distance.
Aspect ratio is simply an indication of the screen format, whether it is widescreen or fullscreen. There are two common aspect ratios: 4:3 (full screen) and 16:9 (widescreen). The numbers indicate the number of units across as compared with the number of units vertically. A 4:3 ratio has four units across for every three units vertically. Aspect ratio is important to note because high-definition content requires a 16:9 widescreen format.
Resolution refers to how many pixels are contained within an image, measured horizontally by vertically. The greater the number of pixels, the clearer the image typically is. The chart below outlines some common resolutions for projectors.
As seen from the chart, high-definition (HD) formats use the widescreen aspect ratio, as does a WXGA resolution, which is technically not HD. Projectors typically have a native, or standard resolution, though they can be set to multiple resolutions for optimal image quality. As such, projectors may support either the 4:3 aspect ratio or a 16:9 ratio. Projectors with support for multiple resolutions and both aspect ratios are more versatile, which is ideal when consumers may use the projector for multiple reasons.
How LCD Projectors Work
LCD, as mentioned above, stands for liquid crystal display. A transmissive technology that creates an image by letting light pass through, LCD panels are widely used in electronics, from the displays on a watch or microwave to television and computer screens. Image creation with an LCD projector first begins with a beam of light. The lamp of the projector shines an intense beam of white light, which then passes to three mirrors, two of which are dichroic mirrors. Unlike a standard mirror that reflects all wavelengths of light (and therefore all colors), a dichroic mirror is designed to reflect only a certain wavelength, and to let the rest of the light pass through. The dichroic mirrors reflect two of the three primary colors (red, blue, or green), leaving the final color to the third mirror.
After the white light is separated into colored beams, each beam is then passed to an LCD panel. An electrical signal arranges the pixels in the LCD panels to recreate the image to be projected. The light passes through the panels, creating three monochrome versions of the image, one red, one blue, and one green. These three separate images then combine inside a prism to create a full-color version that is projected through the lens and onto the screen.
How DLP Projectors Work
DLP, or digital light processing, is a reflective technology that redirects light. It differs from LCD technology in that it uses a tiny chip loaded with microscopic mirrors and aptly named a digital micromirror device, or DMD. Each mirror in the DMD is capable of moving independently and measures no larger than one-fifth the width of a human hair.
As with an LCD projector, image creation in a DLP projector begins with a beam of white light. However, the light shines through a color wheel, a spinning circle that is segmented into red, blue, green, and clear sections. The light takes on the hue of the color wheel segment it passes through and shines on the mirrors. The mirrors adjust to move toward or away from the source of the light as many as several thousand times per second. If a mirror is turned away from the light source more often than it faces the light source, it creates a dark pixel, whereas a mirror that faces the light source more often will create a lighter pixel. The light is then reflected away from the DMD toward the lens, which projects the entire image onto the screen.
Variations on DLP Projectors
Some DLP projectors use color wheels that have more than just red, blue, and green segments. These wheels add cyan, magenta, and yellow segments to allow even more options for color reproduction. Some very high-end models of DLP projectors actually use three DMD chips rather than one. In addition, DLP projectors with LED technology replace the color wheel and lamp entirely, instead using colored light-emitting diodes (LEDs) that shine directly onto the DMD.
Benefits and Shortcomings of LCD and DLP Projectors
DLP and LCD projectors have distinct advantages and disadvantages. For example, while LCD projectors typically create brighter images than comparable DLP projectors, DLP projectors usually have higher contrast ratios. These tradeoffs can affect the images created and the projector design, as well as its performance.
Pros and Cons of LCD Projectors
LCD projectors, as stated above, tend to outperform DLP projectors in terms of image brightness. This is because they are more "light efficient," so an LCD projector with the same wattage as a DLP projector will appear brighter. LCD projectors typically have more accurate color reproduction and better color saturation. Low saturation means the colors appear light and washed out, while a high saturation means bright, vivid hues. LCD projectors also typically have a better sharpness, making them ideal for displaying data, though this sharpness can also create a pixelated effect with video.
LCD projectors use lamp technology with a bulb that needs to be replaced from time to time, typically after 1,000 hours to 5,000 hours of use. This is a large contributing factor to maintenance costs, along with the filters used to keep dust and particles out of the machine. In addition, the LCD panels wear down over time and pixels can burn out, hampering image quality. While consumer-grade LCD projectors are typically less costly than DLP counterparts, replacing a burnt out or damaged LCD panel can be prohibitively expensive.
Pros and Cons of DLP Projectors
DLP projectors can be smaller and lighter than their LCD counterparts, and they have a filter-free design that requires less maintenance. In addition, DLP projectors that use LED technology will likely never need a replacement light source, as LEDs last for longer than the lifetime of the device, sometimes 20,000 hours or more. The DMD chip in a DLP projector is sealed, which prevents dust and particles from settling on it, which protects the image quality. Also, as mentioned above, DLP projectors produce a greater contrast, so blacks appear darker and whites appear brighter.
On the other hand, DLP projectors, especially with slower color wheels, are subject to a "rainbow" effect, which creates flickers of rainbow light on the screen. The mirror technology used can also create a "halo" effect, in which a band of gray light surrounds the screen. Furthermore, DLP projectors without LED technology typically need higher-powered light sources to obtain the same brightness rating, which means they consume more energy. They are also better suited to short-throw environments because they do not usually support zoom lenses.
Buying LCD and DLP Projectors on eBay
When you’re ready to buy an LCD or DLP projector, start by visiting eBay’s Electronics portal. From there, you can navigate to Computers, Tablets, & Networking and select "All Categories." After selecting Monitors, Projectors & Accs and finally Projectors, you can further narrow your results by the type of projection technology, brightness, aspect ratio, and resolution, among other features. In addition, you can simplify the search process by entering a keyword, such as "DLP projector," in the search box on the eBay home page.
Buying and Paying on eBay
If you’re new to eBay, consider stopping by eBay’s Buying Basics section in the Customer Support Center, which walks new shoppers through a variety of processes, such as how to contact a seller and buying options. From here, you can also access other resources, including the All About Buying page, which walks shoppers through the steps from creating an accounting to tracking a purchase.
When buying an item, there are many factors to consider, including payment method. PayPal is fast, easy to use, and accepted by most sellers, making it an ideal choice. PayPal also offers the option of Bill Me Later, a service that allows consumers to buy now and spread payments out over time.
You also may want to consider shipping method. Some sellers offer free or expedited shipping. You can also ask the seller to insure your item when it ships, which protects the item in the event of loss or theft.
DLP and LCD projectors use reflective and transmissive technology, respectively, to display images. In an LCD projector, the light passes through the LCD panel, whereas in a DLP projector, the light is bounced away from a chip with millions of microscopic mirrors. In terms of image quality, LCD projectors have the advantage in color reproduction and saturation, as well as sharpness. DLP projectors have the advantage in terms of contrast, generally offering higher contrast ratios, as well as a less pixelated image that comes from the lower sharpness.
However, there are other factors that differentiate the two kinds of projectors. DLP devices tend to allow for a smaller form factor for easier portability, and they have a filter-less and sealed design that requires maintenance. Some DLP projectors are also equipped with LED technology that gives the light source a longer life than the projector itself. By contrast, LCD projectors require filters and replacement bulbs and can accumulate dust and particles on the panels; the panels also wear down and pixels can burn out over time. However, they are also more light efficient, producing the same brightness level with a lower-powered lamp than a DLP projector. Ultimately, which projector is best for consumers will depend on their needs. When they are ready to buy a projector, eBay is an excellent place to start the search.