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LED display

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This article is about Light-emitting diode (LED) based displays. For LED-backlighted televisions, see LED-backlit LCD television.
The 1,500-foot (460 m) long LED display on the Fremont Street Experience is currently the largest in the world.
The 40m large LED display at the Armin Only event on 19/20 apr 2008 in the Jaarbeurs Utrecht.
The LED Display at the Taipei Arena displays commercials and movie trailers.

A LED display is a video display which uses light-emitting diodes. An LED panel is a small display, or a component of a larger display. They are typically used outdoors in store signs and billboards, and in recent years have also become commonly used in destination signs on public transport vehicles. LED panels are sometimes used as form of lighting, for the purpose of general illumination, task lighting, or even stage lighting rather than display.

Types

There are two types of LED panels: conventional (using discrete LEDs) and surface-mounted device (SMD) panels. Most outdoor screens and some indoor screens are built around discrete LEDs, also known as individually mounted LEDs. A cluster of red, green, and blue diodes is driven together to form a full-color pixel, usually square in shape. These pixels are spaced evenly apart and are measured from center to center for absolute pixel resolution. The largest LED display in the world is over 1,500 ft (457.2 m) long and is located in Las Vegas, Nevada covering the Fremont Street Experience. The largest LED television in the world is the Center Hung Video Display at Cowboys Stadium, which is 160 ft × 72 ft (49 m × 22 m), 11,520 square feet (1,070 m2).

Most indoor screens on the market are built using SMD technology—a trend that is now extending to the outdoor market. A SMD pixel consists of red, green, and blue diodes mounted in a single package, which is then mounted on the driver PC board. The individual diodes are smaller than a pinhead and are set very close together. The difference is that the maximum viewing distance is reduced by 25% from the discrete diode screen with the same resolution.

Indoor use generally requires a screen that is based on SMD technology and has a minimum brightness of 600 candelas per square meter (cd/m², sometimes informally called nits). This will usually be more than sufficient for corporate and retail applications, but under high ambient-brightness conditions, higher brightness may be required for visibility. Fashion and auto shows are two examples of high-brightness stage lighting that may require higher LED brightness. Conversely, when a screen may appear in a shot on a television studio set, the requirement will often be for lower brightness levels with lower color temperatures; common displays have a white point of 6500–9000 K, which is much bluer than the common lighting on a television production set.

For outdoor use, at least 2,000 cd/m² is required for most situations, whereas higher-brightness types of up to 5,000 cd/m² cope even better with direct sunlight on the screen. (The brightness of LED panels can be reduced from the designed maximum, if required.)

Suitable locations for large display panels are identified by factors such as line of sight, local authority planning requirements (if the installation is to become semi-permanent), vehicular access (trucks carrying the screen, truck-mounted screens, or cranes), cable runs for power and video (accounting for both distance and health and safety requirements), power, suitability of the ground for the location of the screen (if there are no pipes, shallow drains, caves, or tunnels that may not be able to support heavy loads), and overhead obstructions.

Flat Panel LED Television Display

Historically, possibly the first true all LED flat panel television TV screen was developed, demonstrated and documented by J. P. Mitchell in 1977.[1] The modular, scalable display was initially designed with hundreds of MV50 LEDs and a newly available TTL memory addressing circuit from National Semiconductor.[2] The ¼ in thin flat panel prototype and the scientific paper were each displayed at the 29th ISEF expo sponsored by the Science Service in Washington D.C. May 1978. The technical display received awards and recognition.[3] Awards included NASA,[4] General Motors Corporation,[5][6] and recognition from faculty and area Universities and the IEEE.[7][8] The event was open to the public including U.S. and foreign representatives. The monochromatic LED prototype remains operational. An LCD (liquid crystal display) matrix design was also cited in the LED paper as an alternative x-y scan technology and as a future alternate television display method. The significance of replacing the 70 year+ high-voltage analog system (cathode-ray tube technology) with a digital x-y scan system has been extremely significant. Displacement of the electromagnetic scan systems included the removal of inductive deflection, electron beam and color convergence circuits. The revolutionary digital x-y scan system has helped the modern television to “collapse” into its current thin form factor.

In 1978, Mitchell also submitted his paper to the Westinghouse Science Talent Search contest, where he received an Honorable Mention.

Mitchell also presented his paper at the 90th Session of The Iowa Academy of Science April 21–22, 1978, at the University of Northern Iowa, Cedar Falls, Iowa.

The 1977 model was monochromatic by design. Efficient blue LEDs did not arrive for another decade. Large displays now use high-brightness diodes to generate a wide spectrum color palette. It took three decades and organic electroluminescent materials for Sony to introduce an actual LED TV: the Sony XEL-1.[9]

See also

References

  1. ^ Mitchell's modular LED x-y (horizontally and vertically digitally scanned array system) was cited in the 29th International Science and Engineering Exposition "book of abstracts", page 97, published by the "Science Service", Washington D.C. May of 1978.
  2. ^ A technical reference detailing the LED display array, RF interface and scanning circuit was included as part of the 1978 29th ISEF exhibition in Anaheim, CA. The original documents are maintained with the early prototype.
  3. ^ The prototype and scientific paper "Light Emitting Diode Television Screen" were part of exhibit #635. The original technical paper is kept with the original working prototype.
  4. ^ Honorable Mention - NASA, 29th ISEF "Announcement of Awards", page 4, Saturday May 13th 1978, published by the Science Service 1719 N Street Washington D.C. 20036.
  5. ^ 3rd Grand Award - GM, corporate sponsor of the 1978 Science Service event. 1978 29th Annual ISEF "Announcement of Awards", page 5, (note: Intel Corporation is the current sponsor of this event).
  6. ^ Contact information: Society for Science & the Public 1719 N Street N.W., Washington, DC 20036, 202-785-2255.
  7. ^ Former IEEE President 1977
  8. ^ Reference; the project witness log, a non-published signature list maintained with the original display materials. A reference listing sponsors and judges: Science Service, 29th ISEF "Program of Events", pages 9, 10 and 11.
  9. ^ Sony marketed the OLED screen in 2009.
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