4 Projector Technologies: Overhead, Opaque , LCD & DLP Projectors

Whether you need to project a page from a book or you want full color video with audio accompaniment, there’s a projector to enhance any presentation.

Let’s start with an overview of the four different kinds of projectors available and what they do.

1. Overhead Projectors

Overhead projectors typically consist of a large box containing a very bright light-source, a fan for cooling the box and a large lens that focuses the light.

Above the box, typically on a long folding arm, is a mirror that redirects the light forward instead of up. Sheets or rolls of transparent film are placed on top of the lens for display. The light from the lamp travels though the transparency and into the mirror where it is reflected onto a viewing screen. The mirror allows an audience to see the image at the same time, even while the presenter is writing.

Overhead projectors were once a common fixture in most classrooms and business meetings. While they’re less popular today, they’re still a great, low-tech way to write notes for large groups in classes, conferences or seminars; it’s much easier and more convenient to write on a flat transparency than a wall-mounted blackboard.

As a result the overhead projector continues to be a popular presentation accessory, and a very economical one as well.

2. Opaque Projectors

The opaque projector was actually the first projector used as a presentation device, before the overhead projector.

The opaque projector displays non-transparent materials (unlike the overhead projector, which uses transparencies) by shining a bright lamp onto the object from above. A system of mirrors, prisms and/or lenses is used to focus the image of the object onto a viewing screen.

Opaque projectors require brighter lamps and larger lenses than overhead projectors. Moreover, care must be taken that the materials are not damaged by the heat generated from the light source.

Early opaque projectors were produced as low cost novelties for children. They were – and are — also marketed to artists, to project enlarged images onto canvases for tracing. Eventually they came into widespread use for lectures and presentations.

Opaque projectors are great for projecting notes, pages from books, photos and artwork, or even thin three-dimensional objects. They are especially useful for art and science classes or seminars.

3. LCD Projectors

LCD (liquid crystal display) projectors are as different from overhead and opaque projectors as a spaceship is different from a car. Where overhead and opaque projectors primarily use 19th century technology (electricity and light bulbs), LCD projectors use liquid crystal panels plus the latest computer and optical technology to project both still and moving images in vivid color.

Many projectors also have built-in audio speakers, making them all-in-one audiovisual presentation units. In general, because LCD projectors are much more sophisticated than overhead projectors, their price points are usually higher.

4. DLP Projectors

Just when it seemed that LCD technology had advanced projectors as far as they could go, along came DLP (digital light processing) projectors.

Where LCD projectors use liquid crystal panels to display images, DLP uses thousands of microscopically small mirrors, which not only move pixels closer together for higher contrast and greater clarity, but also provide greater brightness than LCD projectors. DLP’s high resolution makes it ideal for projecting images or videos in HD. Like LCD projectors, many DLP projectors also feature audio.

Features To Consider When Buying an Overhead or Opaque Projector

Lens Type

The most significant factor in overhead projection image quality is the type of lens being used. The three most common lens types are singlet, doublet and triplet. Image quality increases as you progress from the basic singlet lens type, to the advanced triplet lens type, though price generally increases as well.

Brightness (Lumens)

Each overhead projector is rated on “lumens typical,” which is a standard unit of brightness. For rooms where the ambient light can be lowered, the standard 2,000 lumens will suffice. When you are projecting in a room where ambient light is significant or when projecting complex images (including color), 2,500 lumens or greater is recommended.

Lamp Life

Each overhead projector has an estimated lamp life that is primarily determined by the rating in lumens and lamp type. The common ENX lamp type, for example, offers the longest lamp life while the higher lumens and more specialized nature of other lamp types (FXL, EYB, ENG) offer shorter lamp lives. Because of their intense brightness, these lamps need to be changed frequently – they generally last for less than 100 hours.

Features to Consider When Buying an LCD or DLP Projector


The ratio of the brightest and darkest colors (or blacks and whites) a projector can project is known as the contrast ratio. Any ratio of 400:1 or above should serve you well. LCD projectors generally have contrast ratios of 500:1 or higher, while DLP projectors can go to 2,000:1 or even higher. The higher the ratio, the more vivid and less distorted the images will look.

Brightness (Lumens) & Lamp Life

As with overhead and opaque projectors, brightness is crucial to how well your projector performs. The more lumens, the better! Unlike opaque and overhead projectors, LCD and DLP projector lamps don’t need replacing very often. 2,000 hours and up is typical for lamp life for these projectors.


A projector’s resolution is the number of pixels it displays on the screen. As with contrast and brightness, the bigger the number, the better off you are. Resolution determines how clear your images are and how big you’ll be able to project them without pixelation or distortion. Most projectors employ 1024×768 native resolution.

Video Compatibility

It’s important to know what kind of video a projector can accept before you buy it, especially if you’re using data feeds from international sources. Most LCD and DLP projectors are compatible with the three main types of video: NTSC, PAL and SECAM. Many projectors are also capable of projecting HD video as well.


If you want to make full audiovisual presentations on the road and don’t know whether you’ll have access to an external audio source, then it’s vital to make sure your projector has built-in audio capability. While you’re not going to get glass-shattering power from most projector speakers, you’ll eliminate the need for having to connect hi-fi equipment every time you want to make a presentation.

Still not sure which projector is right for you? Contact our specialists for a free consultation.