Display technologies

The display is the part of the system everyone sees, and the one the customer will judge it by. Four technologies cover almost every commercial AV job. Each makes light — and, just as importantly, makes black — in a different way, and that difference decides where it belongs.

LCD: a backlight and a shutter

An LCD doesn't make its own light. A backlight (today almost always LEDs) shines constantly, and a layer of liquid crystals acts as millions of tiny shutters, opening or closing over each subpixel to let more or less light through colour filters.

Because the shutters can never close completely, some backlight always leaks through, so LCD blacks are really very dark greys. Higher-end panels use local dimming, splitting the backlight into zones that dim behind dark areas. Strengths: affordable, bright, long-lived, no burn-in. This is the default for meeting rooms, classrooms and signage.

OLED: every pixel is a light

In an OLED (organic LED) panel, each subpixel emits its own light. To show black, a pixel simply switches off — so black is truly black, and contrast is effectively unlimited in a dark room. The panels are thin and the picture is superb.

The trade-offs: lower full-screen brightness than high-brightness LCD, a higher price, and burn-in. Pixels age as they emit, so a logo, a ticker or a conferencing interface left on screen for months can leave a permanent ghost.

Direct-view LED: the screen is the light source

A direct-view LED (dvLED) wall is built from tiles or cabinets covered in tiny red, green and blue LEDs. Tiles join with no visible seams, so walls can be built to almost any size or shape. They're extremely bright and handle sunlit lobbies with ease.

Resolution depends on pixel pitch — the distance between LED pixels, in millimetres. A finer pitch packs more pixels into the same area and can be viewed from closer, at a higher cost. dvLED walls also need careful design for power, heat, mounting and service access.

Projection: light thrown onto a surface

A projector forms the image internally — with DLP mirrors, LCD panels or LCoS chips — and throws it onto a screen. Projection is still the most economical way to make a very large image, and modern laser light sources last far longer than the lamps they replaced.

Its weakness is that the screen can't be darker than the room. Every bit of ambient light that reaches the screen raises the black level, and you'll see in lesson three exactly how fast that erodes the picture.

Commercial vs. consumer displays

A TV from an electronics store and a commercial display may share the same panel, but they're built for different lives. Commercial displays are typically chosen for:

• Duty cycle — rated for long daily hours, often up to 24/7, rather than a few hours of evening viewing.
• Control — RS-232 or network control, so a control system can power them on, select inputs and read back their status reliably.
• Installation — portrait mounting, ventilation designed for enclosures, and the ability to lock out the menus and remote.
• Warranty and support — commercial terms that cover installed, business use.

Video walls

When a single panel isn't big enough, LCDs can be tiled into a video wall with ultra-narrow bezels and a processor or built-in controller that spreads one image across them. The thin seams between panels are the trade-off against a seamless — and pricier — dvLED wall.