What Do You Mean by LED?
Light emitting diodes (LEDs) are versatile, energy efficient, and durable. It’s no surprise they’re gaining popularity among a variety of products on the market today. You might be wondering how the LED lights that you see in your kitchen light fixture can possibly be the same lights as the ones that make up your digital signage application. While both applications are referred to with “LED” in the title, the lighting technology is quite different. There are three main types of LEDs that you see in commercial products that are often confused:
In so-called LED TVs (really a misnomer—they are LCD displays with LED backlights), the LEDs are used to shine light thru an LCD display. That is, the LED is placed in back of the LCD—which is why it’s called a “backlight.” The pixels on the LCD display don’t create or emit light themselves—they simply modulate or regulate how much of the light from the LED backlight shines through. In these applications, the LEDs may appear white or maybe a combination of colors to achieve a broader color gamut display.
LEDs are also used in projectors in place of older arc lamps. Similar to an LED backlight on an LCD display, these LEDs for projectors are used as a source of high intensity light (often red, green, and blue LEDs) that is then modulated by a tiny LCD or DMD (digital mirror device) and projected through a lens onto a screen. Sometimes LEDs will be used in conjunction with lasers to create even brighter illumination. In any case, they are a light engine and not the thing creating the image.
LEDs are excellent for architectural lighting because of their high efficiency and long life, as well as their lack of environment-harming mercury. Since LEDs are small, they provide unique design opportunities, which is why you may see them in the form of familiar bulbs or fixtures for general lighting applications. This is the kind of lighting we might use in our homes and offices. These LEDs are optimized for natural white color and for diffuse lighting.
While there is actually no such thing as a “white” LED, common LED colors like amber, red, green, and blue, can be covered with a phosphor material to convert the color of the light to white. Individually, the colors might be seen as signal lights and indicators, like the power button on your computer.
LED displays, also called “direct view LED”, start with the individual LEDs that form the pixels of the display. These can be individual red, green, or blue LEDs (most often in the largest outdoor displays), or they can be single devices that have red, green, and blue (RGB) LEDs integrated together in a single package. The individual LEDs are then attached to a circuit board that is typically referred to as “modules” or “tiles.” Multiple modules are assembled together to form a “cabinet” which is the basic building block of a large LED wall. All of the circuitry, to drive the LEDs and to communicate with the drivers, are part of these modules or connected to them in some fashion. Various architectures are used in such systems, but all result in a modular system that can be assembled together to form a fully scalable display with the gaps between the cabinets hidden within the gaps between the pixels themselves to create a seamless display.
Ultimately, the process to create the LED is similar among all applications, but packaging is what makes the big difference. Some LEDs are packaged to emit more color, more white light, or brighter light than others.
To further the confusion in the market, in North America and Asia the technology is pronounced as the three syllables of the letters LED, “el – ee – dee.” In Europe, they pronounce it “lead” (rhymes with zed, ted, and bed).
To see a full line-up of Leyard and Planar’s LED display offerings, see www.planar.com/products/led-video-walls.