LED DISPLAY TECHNOLOGY

About LED Displays:

Image

 

Image

                                      Unlike traditional media such as newspaper and magazines, LED displays quickly capture attention with a combination of light, color, motion and graphics that get noticed. They also offer infinite options for creating a brand that gets remembered and, in turn, gets results. For most advertisers, the most important market is the local one. Think of LED displays as local advertising and sales partners that are “on” 24/7, working night and day to attract attention, deliver marketing messages and drive sales. LED displays also cost 40 to 60 percent less per thousand viewers than most other forms of advertising. In fact, businesses can communicate with thousands of people each day for just a few dollars. When purchasing an LED display, it is important to understand a few basic principles that will help you select the right product for your application. The following sections present a brief overview of some of these basic principles.

Image

Pitch (Resolution)

Resolution, or the total number of pixels in a display, is a very important factor that affects the performance of the sign. More resolution means more LED diodes and more circuits, which usually means better picture quality.

Pitch is the distance (usually in millimeters) between pixels. Pitch is always measured from the center of one pixel to the center of an adjacent pixel. The smaller the pitch number, the higher the resolution quality. Large  pitch numbers indicate a lower resolution. A pixel can be one single diode, or a pixel can be a cluster of many diodes running off the same circuit.

Viewing Distance and Speed

The distance between your sign and its viewers is the number one factor in determining the type of LED display you will need. Longer distances require less resolution and shorter distances require higher resolutions. In addition, if you are traveling at 55 MPH on a freeway, and the sign is 600 feet away at a truck stop, the text letters must be at least 20 inches tall to be legible. Likewise, if you are standing 60 feet away from a street level sign, the letters need only be two inches tall to be legible.

The rule of thumb is that you need 1 inch for every 30 feet of viewing distance.               

LED Diode Density

LED diode density and pixel pitch are the two most critical factors to determine the quality of resolution and display brightness. LED density of a display is the total number of LED diodes in one square meter. It is calculated by multiplying the number of pixels per square meter by the number of LED diodes per pixel.

Optec Digital Billboards’s LED display systems have always featured more LEDs per pixel than other LED display manufacturers.  Our higher LED diode density provides significantly higher brightness and longer display life since each individual diode can be driven at lower levels of intensity, reserving capacity to extend the display’s life – without sacrificing proper viewing brightness.

Virtual Pixel vs True Pixel

Some LED display manufacturers use “virtual pixel” technology. They claim that “virtual pixel” doubles the actual resolution of screen, i.e., a screen with a physical (true) resolution of 320×240 pixels in reality is expressed as the “virtual” resolution of 640×480.   In a “Virtual Pixel” Display in an attempt to smooth out digital image, each pixel of the image corresponds not to an actual module pixel but to a light/data source, that is part of the group of pixels that form the “Virtual pixel”. By this mode of pixel sharing one pixel contains the “Virtual group”* of pixels image information. *(The 2 or 4 pixels that are combined to form the “Virtual” effect). Virtual pixels are also known as “pixel sharing” or “dynamic pixels”.  Some claim that with “virtual pixels” the displayed image has twice the resolution as the “physical” resolution. This is not true, since one module pixel cannot memorize or hold and display the majority of information from the initial pixel. The majority of the original information vanishes. This results in distortion of important details and other elements such as colors that are part of the initial image.

In the actual, physical or true pixel technology, the image is displayed on a display in as each pixel of the original image corresponds to pixel on a screen.  It takes the actual color in a pixel as it is balanced in brightness and contrast and no additional corrections are required.  Optec Digital Billboards only uses true pixel technology.                                 

Virtual Pixel

Uses pixel sharing to achieve “virtual” pitch.Attempts to achieve equal resolution using 1/4 the diodes of a true pixel display.                                                               

True Pixel

Each pixel is distinct, using individual groups of LEDs.  Display has 4x the diode density of a virtual pitch, resulting in 4x brightness, greater color depth and better color accuracy.          

Brightness

The Brightness of an LED display is generally expressed by a numerical value in NITs. A NIT is defined as unit of illuminative brightness described as candela output per square meter (cd/M2). The higher the number of NITs, the brighter the display. In general, 1,500 NITs, provides readable text in outdoor daylight, while grayscale and outdoor video require up to 5,000 NITs for acceptable color depth.

Optec Digital Billboards displays are built with a high-density of super-bright, high quality LED diodes, so our displays typically exceed this standard by a long shot. Contrast ratio is another important factor in overall brightness, and refers to the difference between levels of blacks compared to the levels of whites in the display. Things like reflective surfaces, glare from the sun, and dimming all affect contrast ratio. To optimize the contrast ratio and overall brightness, Optec Digital Billboards displays feature a unique louver system to shade each individual diode from the glare of the sun. The louvers were computer modeled to optimize the view from onlookers below while blocking the maximum amount of sun from all sides. No other system on the market offers this unique, individual diode shading. Together with the high-density array, Optec Digital Billboards displays are truly the brightest, longest lasting product on the market today.

Viewing Angle

Diodes can put out a single, narrow beam of light like a flashlight, or they can output a wide array across a room like a light bulb. Diodes output about the same amount of light no matter what type they are – but the “high-beam” diodes with a narrow angle focus more light into one small spot, whereas the “wide angle” diodes spread their light across the horizon. So, if you were to stand in front of a sign made from “high-beam” diodes with narrow viewing angles, you would see an extremely bright sign if you stood directly in front of it, but the minute you walked away from the small spot light of its focus, you would see nothing but black.

With wide viewing angle LEDs, the image is visible in consistent brightness and uniform colors throughout the entire viewing range of the display.  Optec Digital Billboards only uses wide angle 1400 LEDs to maximize audience exposure, maintain the highest color accuracy and extend reading times.  Maintaining brightness across a wide spectrum also requires greater light output, which is why Optec Digital Billboards uses a higher LED diode density than any other manufacturer in the industry.

LED Overview

LEDs differfrom traditional light sources in the way they produce light. In an incandescent lamp, atungsten filament is heated by electriccurrent until it glows or emits light. In a fluorescent lamp, anelectric arc excites mercury atoms, which emit ultraviolet (UV)radiation.

A light emitting diode, in contrast, is made from a chip of semiconducting material in a way that when connected to a power source, current flows in one direction but not the other. When currentflows through the diode, energy is released in the form of a photon (light). The specific wavelengthor color emitted by the LED depends on the materials used to make the diode.

Red LEDs are based on aluminum gallium arsenide (AlGaAs). Blue LEDs are made from indium gallium nitride (InGaN) and green from aluminum gallium phosphide (AlGaP).  White light is created by combining the light from red, green, and blue

Image

(RGB) LEDs or by coating a blue LED withyellow phosphor. OCS displays in use today utilize red LEDs.

To make a readable display from LEDs, they are arranged in a matrix as shown below. The matrix isconfigured with sufficient number of LEDs to allow alphanumeric characters to be formed byilluminating specific patterns.

Image

Wide Temperature Operation –  LEDs have wider temperature operating limits; however their brightness and expected lifetime falls off significantly with heat. Red LEDs, utilized in OCS products on the market

today perform worst, falling off to 40% of brightness at 100°C.

Image

Pixel Pitch – Due to the relatively large size of individual LEDs, they inherently have farfewer pixelsper inch than LCDs (17:1 ratio of LCD pixels to LED pixels for the same size display area).Accordingly, they are not optimal for displaying pictures, international language characters or complex figures when viewed at close range as with OCS applications.

Number of Colors – As mentioned above, red LEDs are typically used in OCS equipment in the field today. A single color limits the amount of information that can be conveyed to the customer.Additionally, red is not the optimum color for high contrast readability in direct sunlight.

Graphic Display Capability – LEDs (as used in OCS equipment today) are limited to displaying simple alpha numeric characters and have no graphic display  capability.

International Characters LEDs used in OCS equipment today cannot support complex multi byte international language character fonts due to their inherent limitation in resolution.

Flexibility of Display Layout – OCS LED displays are arranged as a fixed number of rows and columns of fixed size characters, allowing no flexibility in the layout of the display.

Cost – Due to the simplicity of the design of LED based OCS displays, they are typically lower cost  than LCD based OCS displays.

 

 

 

 

 

Advertisements